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Hindawi Publishing CorporationJournal of MaterialsVolume 2013 Article ID 191626 6 pageshttpdxdoiorg1011552013191626

Research ArticleGrowth and Neutron Diffraction Investigation ofCa3NbGa3Si2O14 and La3Ga55Nb05O14 Crystals

I A Kaurova1 G M Kuzrsquomicheva2 V B Rybakov3 A Cousson4

O Zaharko5 and E N Domoroshchina2

1 Moscow State Open University 3 Entuziastov Street Aleksandrov 601655 Russia2 Lomonosov Moscow University of Fine Chemical Technology 86 Vernadskogo Prospekt Moscow 119571 Russia3 Lomonosov State University Vorobyovy Gory Moscow 119992 Russia4 Laboratoire Leon Brillouin CeaSaclay 91191 Gif-sur-Yvette Cedex France5 Laboratory for Neutron Scattering ETZ Zurich amp Paul Scherrer Institute (PSI) CH 5232 Villigen Switzerland

Correspondence should be addressed to I A Kaurova kaurchikyandexru

Received 27 November 2012 Accepted 6 February 2013

Academic Editor Necmettin Maraslı

Copyright copy 2013 I A Kaurova et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Langanite (La3Ga55Nb05O14 growth atmosphere 99 Ar + 1 O

2) and kanigasite (Ca

3NbGa

3Si2O14 growth atmosphere 100

Ar) crystals grown by the Czochralski technique in Ir crucibles along lt0001gt direction have been firstly investigated by neutrondiffraction The difference between the compositions of upper (La

2935(2)◻

0065)(Ga0450

Nb0550(3)

)Ga3(Ga1965(4)◻

0035)(O1390(1)◻

010)

and lower (La2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018) parts of orange langanite crystal was found It was established that

the colorless Ca3NbGa

3Si2O14

crystal grown by using the single-crystal charge has the composition (Ca295◻

005(1))NbGa

3Si2O14

and is less defective in comparison to the yellow one grown by using the charge prepared by conventional solid-state reaction ForCa3NbGa

3Si2O14and La

3Ga55Nb05O14crystals the possibility of microtwin formation (two unit cells connected by the translation

12 z) was revealed for the first time It was found that the difference between the color of crystals is attributed to the qualitativedifferentiation of oxygen vacancies

1 Introduction

Kanigasite (Ca3NbGa

3Si2O14 CNGS) and langanite (La

3

Ga55Nb05O14 La3(Ga05Nb05)Ga5O14 LGN) crystals have

langasite-type structure (spgr P321 119885 = 1) similar tolangasite (La

3Ga5SiO14 La3Ga4(GaSi)O

14 LGS) and lan-

gatate (La3Ga55Ta05O14 La3(Ga05Ta05)Ga5O14 LGT) ones

Langasite family crystals possess a number of propertiesthat ensure the successful application in piezo- opto- andacoustoelectronics These properties include the absence ofstructural phase transitions up to the melting temperaturehigh thermal stability high values of electromechanical cou-pling coefficients and acoustic119876 and low loss propagation ofthe elastic waves in the crystal Langanite is characterized bythe largest values of piezoelectric modules (119889

11= minus741 plusmn

02 CN 11988914= 616 plusmn 05 CN) [1] among the langasite

family crystals whereas the CNGS has high values of the

acoustic quality factor (119876 = 56000) due to the fact that everyatom in its structure is located in an individual position Thecrystallographic orientation with a zero TCF (temperaturecoefficient of frequency) at room temperature was foundfor this crystal The traditional Czochralski method is theprimary method of obtaining large-size LGN [2ndash7] andCNGS [6ndash16] single crystals up to 200mm in diameter

However the use of these compounds depends on thecomposition (in other words on the type and concentrationof point defects) which does not coincide with the composi-tion of the initial chargeThere are quite a few works devotedto the structural investigation of CNGS [6 8 11] and LGN[6 17 18] crystals All of them were performed using X-rayand the occupancies were refined only in some cases In theliterature there are no results of neutron investigation of LGNand CNGS crystals as the most correct to identify defects inthe crystallographic positions in particular oxygen ones

2 Journal of Materials

Neutron diffraction investigations of langasite [19] andlangatate [20ndash22] single crystals have revealed that the pointdefects are present in all positions of the structure Inaddition the relationship between the crystal color and theoxygen vacancies contents has been established Probablythe other crystals with langasite-type structure in particularLGN and CNGS will have the same relationship

The aim of this work is to determine the compositions ofCNGS and LGN crystals grown by the Czochralski techniqueusing neutron diffraction

2 Experimental Technique

Ca3NbGa

3Si2O14and La

3Ga55Nb05O14

crystals were grownby the Czochralski technique along lt0001gt direction in aKristal-3M growth system in Ir crucible (ℎ = 120mm119889 = 120mm the thickness of wall and the bottom 119904 =2mm) using a pure Ar (CNGS) or 99-98 Ar + 1-2O2(LGN) growth atmospheres The pulling rate was 1ndash

3mmh and the crystal rotation rate was 1ndash10 rpm TheCNGS and LGS seeds were used for Ca

3NbGa

3Si2O14

and La3(Ga05Nb05)Ga5O14

crystals growth respectivelyEither crushed CNGS single crystal (crystal 1) or polycrys-talline material prepared by conventional solid-state reaction(Al2O3crucible 119879 sim 1300∘C 6 hours) (crystal 2) was used

for growth of two CNGS crystals Starting materials wereprepared by mixing of 9999 pure La

2O3 Ga2O3 Nb2O5

SiO2 and CaCO

3powders at the stoichiometric ratio A

single-crystal charge was used for La3(Ga05Nb05)Ga5O14

crystal growthThe colorless (crystal 1) and yellow (crystal2) Ca

3Nb

Ga3Si2O14

crystals 50mm in diameter with 80mm longcylindrical portion [23] as well as the orange La

3Ga55

Nb05O14

crystal 30mm in diameter with 100mm long cylin-drical portion [24] were grown by theCzochralski techniqueAll the crystals were transparent The faceting of the crystalswas represented by poorly pronounced faces of the hexagonalprism

The CNGS samples under investigation represent theupper parts of colorless (CNGS-1) and yellow (CNGS-2) singlecrystals (Figures 1(a) and 1(b)) Orange LGN samples werecut from the top (LGN-1 LGN-11015840) and bottom (LGN-2) of thecrystal (Figures 2(a) and 2(b)) It should be noted that theupper parts (LGN-1LGN-1 1015840) had amore intense orange color

The neutron diffraction analysis (NDA) of LGN-1 (sizesim43 times 4 times 5mm) and CNGS-2 (size sim4 times 4 times 4mm)samples was carried out at room temperature on the four-circle diffractometer installed at the hot source (5C2) of theOrphee reactor (LLB France 120582 = 083 A 120596-scan mode)and investigation of CNGS-1 (size sim3 times 4 times 4mm) LGN-11015840 (size sim4 times 4 times 4mm) and LGN-2 (size sim4 times 4 times45mm) samples was performed at room temperature on thefour-circle single-crystal TriCS diffractometer (Paul ScherrerInstitute Switzerland 120582 = 118 A 120596-scan mode)

TheX-ray diffraction analysis (XRD) ofCNGS-2microre-gion sim03 times 03 times 03mm was carried out on a CAD-4 four-circle diffractometer at room temperature (MoK

120572radiation

graphite monochromator 120596-scan mode)

The crystal structure (atomic coordinates occupancies ofall positions) was refined using the full-matrix least squaresprocedure in the anisotropic approximation for all atomswithSHELXL-97 program package [25]

3 Results and Discussions

In the Ca3NbGa

3Si2O14structure each atom is located in the

individual position Ca in the dodecahedral (position 3e)Nb in the octahedral (position 1a) Ga in the tetrahedral(position 3f ) and Si in a trigonal-pyramidal (position 2d)[8] While in the La

3(Ga05Nb05)(1)Ga

3(2)Ga

2(3)O14crystals

lanthanum atoms are in the dodecahedral position of thestructure and gallium atoms occupy octahedral (Ga Nb)(1)position half replaced by the niobium atoms tetrahedralGa(2) and trigonal-pyramidal Ga(3) ones [17]

31 Ca3NbGa

3Si2O14

Crystals According to the neutrondiffraction data obtained (Table 1) CNGS-1 cut from the col-orless crystal has a composition (Ca

295◻

005(1))NbGa

3Si2O14

with vacancies (◻) located in the Ca position-119881ca10158401015840 The

deficiency of other positions as well as their occupation bythe other atoms (antistructural defects) was not detectedDue to the fact that the electroneutrality condition for therefined composition is not satisfied we assumed that a certainnumber of Ca2+ ions in the structure are interstitial onesas for the (La

2964◻

0036)Lai(0036)Zr05Ga5Si05O14 [26] The

analysis of the residual nuclear density does not excludesuch possibility The peak with the coordinates 119909 = 0464119910 = 0069 and 119911 = 0136 close to the interstitial Lai atomcoordinates (119909 = 0418 119910 = 0009 and 119911 = 0139) [26] wasfound Interstitial Cai atoms (like Lai atoms) are displacedfrom the dodecahedral positions approaching one of fouroxygen atoms thus forming two reduced CandashO (sim 206 A)and two increased distances According to Bokiy [27] ldquotheapparent size of the interstitial atomsdepends on their relativequantity the smaller relative quantity of dissolved non-metalthe smaller the apparent size of its atomsrdquo

Thereby it allow us to rewrite the CNGS-1 crystal compo-sition as (Ca

295◻

005(1))Cai(005)NbGa3Si2O14

Refining the structure of CNGS-2 cut from the yellowcrystal by direct methods allows revealing both atomiccoordinates similar to CNGS-1 ones (the unit cell 1) andatomic coordinates associated with the previous ones by thetransition matrix 10001000z+05 (the unit cell 2) Boththese unit cells are present in structure of CNGS-2 crystalin the ratio of unit cell 1 unit cell 2sim4 1 (Table 2) For thestructure determination the atomic coordinates of CNGS-1were taken as the initial ones However as a result of thecalculation fairly strong peaks of the residual nuclear densitywere foundThe coordinates of peaks correspond to a crystalmodel with a shift 12 zThe refinement of the structure usingthe second model (the initial coordinates are shifted by 12along the z-axis) based on electron density maps led to theappearance of strong peaks of the residual nuclear densitywith the coordinates of the initialmodel (without shift)Theseexperimental results suggest the existence of the translationtwin (like racemic twins) at the level of elementary cells In

Journal of Materials 3

(a) (b)

Figure 1 Photo of the samples CNGS1 (a) and CNGS2 (b)

(a) (b)

Figure 2 Photo of the samples LGN1 (a) and LGN2 (b)

other words in CNGS-2 structure there are two unit cellswhich can be connected with the transition 12 z Therebythe volume defect of the crystal structure (translation twin) ispresent in some regions of the CNGS-2 sample Such a defecthas not been previously met for langasite family crystals

According to our results of X-ray diffraction analysis(XRD) which were used for the refinement of the crystalstructure ofCNGS-2 sample amicroregion has a compositionCa3NbGa

3(Si1985◻

0015(10))(O1397(3)◻

003) (1198771= 523) with

vacancies in trigonal-pyramidal (119881Si1015840101584010158401015840) and oxygen (119881O

∙∙)positions

Takeda et al [5] and Kimura et al [28] have suggestedthat the color of langasite family crystals depends onmaterialof the crucible in particular Ir However the orange LGNand colorless CNGS have been grown using both Pt and Ircrucibles under the same growth conditions It should benoted that according to [29] the crystal color cannot be asso-ciated with the presence of iridium in the composition of thecrystal because according to the inductively coupled plasmaatomic emission spectroscopy data the iridium content in thecolored crystals is lower than 1 ppm It can be assumed thatthe Ir content less than 1 ppm can cause the yellow color of

CNGS crystal However the crystal growth in Pt crucibles atthe same growth conditions as growth in the Ir crucible leadsto the orange color of the crystals too Thus the influenceof crucible material on color of LGN and CNGS is quitecontroversial

Kuzrsquomicheva et al [20 22] Kaurova et al [21] andDomoroshchina et al [29] have reported using X-ray orneutron diffraction analysis that the LGS and LGT crystalscolor depends on the presence of oxygen vacancies in thestructure of crystals that is the absence of color for thiscrystals is due either to the absence of oxygen vacancies or totheir large content Thus the light yellow and yellow crystalsas well as the colorless ones are characterized by differentcompositions of oxygen positions [21 22]

According to our data [21 22] and the literature data[30] the annealing in vacuum of the orange crystal causes itsdiscoloring It is accompanied by oxygen vacancies contentincreasing in the crystal structure [21 22] Annealing inair of the same crystal leads to more saturated color tones[21 22 30] It is accompanied by decreasing the content ofoxygen vacancies [21 22] In turn colorless crystals grown inargon and treated in vacuum do not change their color [30]


Table 1 Refined compositions of Ca3NbGa

3Si2O14and La

3Ga55Nb05O14crystals according to the results of the neutron diffraction analysis

(NDA)

Crystal Unit cell parameters A119886 119888 Refined composition (NDA)

CNGS-1 80911 (2)49811 (1)

(Ca295◻

005(1))NbGa

3Si2O14

119877 = 415

LGN-1 82283 (4)51268 (3)

(La2935(2)◻

0065)(Ga0450

Nb0550(3)

)Ga3(Ga1965(4)◻

0035)(O1390(1)◻

010)

119877 = 810

LGN-2 82293 (3)51272 (2)

(La2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)

119877 = 724

Table 2 The atom coordinates in two-twinned unit cell of CNGS-2crystal

CNGS-2Parameter

Unit cell 1 Unit cell 2119909 0 0

Ca 119910 05724 05936119911 0 05119909 0 0

Nb 119910 0 0119911 0 05119909 0 0

Ga 119910 02334 02501119911 05 0119909 13 13

Si 119910 23 23119911 04710 09700119909 13 13

O(1) 119910 23 23119911 01853 07245119909 01352 01553

O(2) 119910 04529 04489119911 03069 07638119909 02255 02553

O(3) 119910 01566 01511119911 02404 07638

The results of NDA and XRD investigations of theCNGS crystals confirm these conclusions The color ofCa3NbGa

3Si2O14

is also caused by the oxygen vacancieswhich are absent in the structure of the colorless crystal 1 Itis not excluded that the annealing of crystals in the air willweaken their color will reduce the quantity of point defectsand will improve their optical properties as it was observedfor langasite crystals [31] According to our results onlyoxygen vacancies which depend on growth and treatmentconditions take part in color centers formation

Thus the colorless Ca3NbGa

3Si2O14

crystal (crystal 1)grown by using the single-crystal charge is structurallymore perfect in comparison with the yellow one (crystal 2)grown by the charge prepared by conventional solid-state

reaction In this way colorless Ca3NbGa

3Si2O14

crystal ismore preferred for the practical application in piezoelectricand acoustic-electronic devices The results of the dielectricproperties investigations of CNGS crystals are the confirma-tion of this conclusion For the colorless crystals the valuesof relative dielectric constants are higher compared with theones for the yellow crystals [16 32]

The same (upper) parts of crystals 1 and 2 were investi-gated by the diffraction methods The compositions of theupper part of the crystal growing from polycrystalline chargediffer from those of the lower part [19] If this crystal willbe crushed and regrown the composition will probably beaveraged and oxygen content will be increased

32 La3Ga55Nb05O14

Crystals According to the neutrondiffraction data obtained (Table 1) the composition ofthe upper part LGN-1 of La

3Ga55Nb05O14

crystal canbe written as (La

2935(2)◻

0065)(Ga0450

Nb0550(3)

) Ga3

(Ga1965(4)◻

0035)(O1390(1)◻

010) that is with Nb gt Ga

in the octahedral position (GaNb)(1) and with vacancies inthe dodecahedral (119881La

101584010158401015840) and trigonal-pyramidal (119881Ga101584010158401015840)

positions and in the oxygen (119881O∙∙) one The atomic

coordinates which were used for the LGN-1 calculation wasalso used for the refinement of the crystal structure andcomposition of the LGN-1 sample cut from the top of thecrystal The refined composition of LGN-11015840 can be writ-ten as (La

2940(2)◻

0060)(Ga0485

Nb0515(6)

)(Ga2940(2)◻

0060)Ga2

(O1384(1)◻

016) (119877 = 1002) The compositions of the LGN-1

and LGN-1 1015840 samples are in good agreement with each otherHowever for the LGN-1 1015840 sample as well as for the CNGS-2sample sufficiently strong peaks of the residual electrondensity with coordinates associated with the found ones bythe transition matrix 10001000z+05 were revealed Italso indicates the defect structure of the upper part of theLa3Ga55Nb05O14

crystal what can be connected with theusing of LGS as a seed

The lower part of the crystal (LGN-2) has a com-position (La

2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)

with vacancies located in the dodecahedral (119881La101584010158401015840) and the

oxygen (119881O∙∙) positions and with Ga gt Nb in the octahedral

position (Ga Nb)(1)Thus according to the neutron diffraction data obtained

there are the same types of point defects (the vacancies inthe lanthanum and oxygen positions) in the compositionsof the top and the bottom of the La

3Ga55Nb05O14

crystal


Different ratios of GaNb and of oxygen vacancies concen-trations (Table 1) indicate the composition and propertiesinhomogeneity over the volume of the crystal It is notexcluded that the LGN crystal color is also attributed tothe qualitative differentiation of oxygen vacancies present inthe structures In orange crystals (LGN-1 LGN-11015840) a higheroxygen content was found In our opinion the relationshipbetween color and oxygen content for LGN must be thesame as for LGT [21 22] and LGS [29] For example thecolor of the crystals of composition La

3(GaTa5+)Ga

5O119910

varies depending on oxygen content (the neutron diffractionresults) 119910 = 13872(6) is colorless crystal 119910 = 13918(7)yellow crystal 119910 = 13969(8) orange crystal 119910 = 13975(6)light yellow crystal and 119910 = 140 colorless crystal thatis the colorless crystals may be characterized either by theabsence of oxygen vacancies or by their large content [21 22]The reason of crystal color is believed to be the color centerformation (119881O

n∙ ne1015840)times119881On∙gt (119881O

n∙ ne1015840)times colorless crystalsand 119881O

n∙lt (119881O

n∙ ne1015840)times colored crystals

4 Conclusions

The colorless and yellow Ca3NbGa

3Si2O14

crystals (growthatmosphere 100 Ar) and orange La

3(Ga05Nb05)Ga5O14

crystal (growth atmosphere 99Ar + 1 O2) were grown

by the Czochralski technique in the Ir crucible along lt0001gtgrowth direction The results of the neutron diffractioninvestigations of this crystals are reported

It was established that the using of single-crystal charge isnecessary for the growth of structural quality crystals

The difference between the compositions of top andbottom of La

3Ga55Nb05O14

crystal was found The poorstructural quality of La

3Ga55Nb05O14

crystal upper part isdue to the using of La

3Ga5SiO14crystal as a seed

The possibility of microtwins formation (two unit cellsconnected by the translation 12 z) was revealed forCa3NbGa

3Si2O14and La

3(Ga05Nb05)Ga5O14crystals

It was found that the color of the Ca3NbGa

3Si2O14

andLa3(Ga05Nb05)Ga5O14

crystals is caused by oxygen vacan-cies present in the structures like the La

3(Ga05Ta05)Ga5O14

and La3Ga4(GaSi)O

14crystals

References

[1] J Bohm E Chilla C Flannery et al ldquoCzochralski growth andcharacterization of piezoelectric single crystals with langasitestructure La

3Ga5SiO14

(LGS) La3Ga55Nb05O14

(LGN) andLa3Ga55Ta05O14(LGT) II Piezoelectric and elastic propertiesrdquo

Journal of Crystal Growth vol 216 no 1 pp 293ndash298 2000[2] B V Mill and Y V Pisarevsky ldquoLangasite-type materials from

discovery to present staterdquo in Proceedings of IEEE InternationalFrequency Control Symposium and Exhibition pp 133ndash144 June2000

[3] T Fukuda H Takeda K Shimamura et al ldquoGrowth of newlangasite single crystals for piezoelectric applicationsrdquo in Pro-ceedings of the 11th IEEE International SymposiumonAppliationsof Ferroelectrics (ISAF-XI) pp 315ndash319 August 1998

[4] J Bohm R B Heimann M Hengst R Roewer and JSchindler ldquoCzochralski growth and characterization of piezo-electric single crystals with langasite structure La

3Ga5SiO14


(LGN) and La3Ga55Ta05O14

(LGT)Part Irdquo Journal of Crystal Growth vol 204 no 1 pp 128ndash1361999

[5] H Takeda K Shimamura T Kohno and T Fukuda ldquoGrowthand characterization of La

3Nb05Ga55O14single crystalsrdquo Jour-

nal of Crystal Growth vol 169 no 3 pp 503ndash508 1996[6] G M Kuzmicheva E N Domoroschina V B Rybakov A B

Dubovsky and E A Tyunina ldquoA family of langasite growth andstructurerdquo Journal of Crystal Growth vol 275 no 1-2 pp e715ndashe719 2005

[7] B H T Chai A N P Bustamante and M C Chou ldquoA newclass of ordered langasite structure compoundsrdquo in Proceedingsof IEEE International Frequency Control Symposium and Exhi-bition pp 163ndash168 June 2000

[8] B V Millrsquo E L Belokoneva and T Fukuda ldquoNew compoundswith a Ca

3Ga2Ge2O14-type structure A

3XY3Z2O14(A = Ca Sr

Ba Pb X = Sb Nb Ta Y = Ga Al Fe In Z = Si Ge)rdquo RussianJournal of Inorganic Chemistry vol 43 no 8 pp 1168ndash1175 1998

[9] M M C Chou S Jen and B H T Chai ldquoNew ordered lan-gasite structure compoundsmdashcrystal growth and preliminaryinvestigation of the material propertiesrdquo in Proceedings of IEEEUltrasonics Symposium pp 225ndash230 October 2001

[10] T Karaki R Sato M Adachi J I Kushibiki and M ArakawaldquoPiezoelectric properties of Ca

3NbGa

3Si2O14

single crystalrdquoJapanese Journal of Applied Physics B vol 43 no 9 pp 6721ndash6724 2004

[11] I H Jung A Yoshikawa T Fukuda and K H Auh ldquoGrowthand structure of A

3NbGa

3Si2O14

(A=Sr Ca) compoundsrdquoJournal of Alloys and Compounds vol 339 no 1-2 pp 149ndash1552002

[12] I H Jung Y H Kang K B Shim A Yoshikawa T Fukudaand K H Auh ldquoSingle crystal growth and characterizationsof A3NbGa

3Si2O14-type compounds for piezoelectric applica-

tionsrdquo Japanese Journal of Applied Physics B vol 40 no 9 part1 pp 5706ndash5709 2001

[13] ZWangD YuanDXu et al ldquoGrowth anddielectric propertiesof Ca3NbGa

3Si2O14crystalsrdquo Journal of Alloys and Compounds

vol 370 no 1-2 pp 291ndash295 2004[14] Z Wang X Cheng D Yuan et al ldquoCrystal growth and prop-

erties of Ca3NbGa

3Si2O14

single crystalsrdquo Journal of CrystalGrowth vol 249 no 1-2 pp 240ndash244 2003

[15] Z Wang D Yuan A Wei et al ldquoGrowth and optical activity ofCa3NbGa

3Si2O14single crystalrdquo Applied Physics A vol 78 no

4 pp 561ndash563 2004[16] X Shi D Yuan X Yin S Guo X Zhang and Z Li ldquoCrystal

growth and dielectric piezoelectric and elastic properties ofCa3NbGa

3Si2O14single crystalrdquo Journal of Crystal Growth vol

293 no 2 pp 485ndash488 2006[17] A A Kaminskii B V Mill E L Belokoneva C E Sarkisov

T Y Pastukhova and G G Khogzhabagyan ldquoCrystal structureand stimulated emission La

3Ga55Nb05O14mdashNd3+rdquo Journal of

Inorganic Materials vol 20 pp 2058ndash2061 1984 (Russian)[18] T S Chernaya S S Kazantsev V N Molchanov et al ldquoCrystal

structure of La3Nb05Ga55O14at 20 Krdquo Crystallography Reports

vol 51 no 1 pp 23ndash28 2006[19] G M Kuzrsquomicheva O Zakharko E A Tyunina V B Rybakov

E N Domoroshchina and A B Dubovski ldquoNeutron diffrac-tion and X-ray diffraction investigations of langasite crystalsrdquoCrystallography Reports vol 53 no 6 pp 989ndash994 2008

[20] G M Kuzrsquomicheva O Zaharko E A Tyunina et al ldquoPointdefects in langatate crystalsrdquo Crystallography Reports vol 54no 2 pp 279ndash282 2009


[21] I A Kaurova G M Kuzrsquomicheva V B Rybakov A BDubovskii and A Cousson ldquoComposition structural param-eters and color of langataterdquo Inorganic Materials vol 46 no 9pp 988ndash993 2010

[22] G M Kuzrsquomicheva I A Kaurova V B Rybakov et al ldquoThecolor of langatate crystals and its relationship with compositionand optical propertiesrdquoCrystal Research and Technology vol 47no 2 pp 131ndash138 2012

[23] I A Kaurova G M Kuzrsquomicheva V B Rybakov A BDubovsky A Cousson andO Zaharko ldquoGrowth and structuralinvestigations of Ca

3NbGa

3Si2O14

crystalsrdquo KhimicheskayaTechnologiya vol 11 no 10 pp 585ndash591 2010 (Russian)

[24] G M Kuzrsquomicheva E A Tyunina E N Domoroshchina VB Rybakov and A B Dubovskii ldquoX-ray diffraction study ofLa3Ga55Ta05O14and La

3Ga55Nb05O1414 langasite-type single

crystalsrdquo Inorganic Materials vol 41 no 4 pp 412ndash419 2005[25] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-

graphica A vol 64 no 1 pp 112ndash122 2007[26] A A Pugacheva B A Maksimov B V Millrsquo et al ldquoGrowth

and structure of La3Zr05Ga5Si05O14

crystalsrdquo CrystallographyReports vol 49 no 1 pp 53ndash59 2004

[27] G B Bokiy Introduction to Crystal Chemistry MGU MoscowRussia 1954

[28] H Kimura S Uda O Buzanov X Huang and S Koh ldquoTheeffect of growth atmosphere and Ir contamination on electricproperties of La

3Ta05Ga55O14single crystal grown by the float-

ing zone and Czochralski methodrdquo Journal of Electroceramicsvol 20 no 2 pp 73ndash80 2008

[29] E N Domoroshchina G M Kuzrsquomicheva V B Rybakov AB Dubovsky E A Tyunina and S Y Stepanov ldquoRelationshipbetween growth conditions structure and optical properties oflangasite crystals La

3Ga5SiO14rdquo PerspectiveMaterials vol 4 pp

17ndash30 2004 (Russian)[30] O A Buzanov E V Zabelina andN S Kozlova ldquoOptical prop-

erties of lanthanum-gallium tantalate at different growth andpost-growth treatment conditionsrdquo Crystallography Reportsvol 52 no 4 pp 691ndash696 2007

[31] E A Tyunina G M Kuzrsquomicheva O Zaharko and A BDubovsky ldquoEffect of growth and post-growth treatment condi-tions on langasite crystals optical propertiesrdquo Vestnik MITHTvol 5 no 5 pp 27ndash35 2010 (Russian)

[32] M Adachi T Funakawa and T Karaki ldquoGrowth of substi-tuted langasite-type Ca

3NbGa

3Si2O14single crystals and their

dielectric elastic and piezoelectric propertiesrdquo in Proceedingsof the 13th IEEE International Symposium on Applications ofFerroelectronics (ISAF rsquo02) pp 411ndash414 June 2002

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materials


Journal ofNanomaterials


Neutron diffraction investigations of langasite [19] andlangatate [20ndash22] single crystals have revealed that the pointdefects are present in all positions of the structure Inaddition the relationship between the crystal color and theoxygen vacancies contents has been established Probablythe other crystals with langasite-type structure in particularLGN and CNGS will have the same relationship

The aim of this work is to determine the compositions ofCNGS and LGN crystals grown by the Czochralski techniqueusing neutron diffraction

2 Experimental Technique

Ca3NbGa

3Si2O14and La

3Ga55Nb05O14

crystals were grownby the Czochralski technique along lt0001gt direction in aKristal-3M growth system in Ir crucible (ℎ = 120mm119889 = 120mm the thickness of wall and the bottom 119904 =2mm) using a pure Ar (CNGS) or 99-98 Ar + 1-2O2(LGN) growth atmospheres The pulling rate was 1ndash

3mmh and the crystal rotation rate was 1ndash10 rpm TheCNGS and LGS seeds were used for Ca

3NbGa

3Si2O14

and La3(Ga05Nb05)Ga5O14

crystals growth respectivelyEither crushed CNGS single crystal (crystal 1) or polycrys-talline material prepared by conventional solid-state reaction(Al2O3crucible 119879 sim 1300∘C 6 hours) (crystal 2) was used

for growth of two CNGS crystals Starting materials wereprepared by mixing of 9999 pure La

2O3 Ga2O3 Nb2O5

SiO2 and CaCO

3powders at the stoichiometric ratio A

single-crystal charge was used for La3(Ga05Nb05)Ga5O14

crystal growthThe colorless (crystal 1) and yellow (crystal2) Ca

3Nb

Ga3Si2O14

crystals 50mm in diameter with 80mm longcylindrical portion [23] as well as the orange La

3Ga55

Nb05O14

crystal 30mm in diameter with 100mm long cylin-drical portion [24] were grown by theCzochralski techniqueAll the crystals were transparent The faceting of the crystalswas represented by poorly pronounced faces of the hexagonalprism

The CNGS samples under investigation represent theupper parts of colorless (CNGS-1) and yellow (CNGS-2) singlecrystals (Figures 1(a) and 1(b)) Orange LGN samples werecut from the top (LGN-1 LGN-11015840) and bottom (LGN-2) of thecrystal (Figures 2(a) and 2(b)) It should be noted that theupper parts (LGN-1LGN-1 1015840) had amore intense orange color

The neutron diffraction analysis (NDA) of LGN-1 (sizesim43 times 4 times 5mm) and CNGS-2 (size sim4 times 4 times 4mm)samples was carried out at room temperature on the four-circle diffractometer installed at the hot source (5C2) of theOrphee reactor (LLB France 120582 = 083 A 120596-scan mode)and investigation of CNGS-1 (size sim3 times 4 times 4mm) LGN-11015840 (size sim4 times 4 times 4mm) and LGN-2 (size sim4 times 4 times45mm) samples was performed at room temperature on thefour-circle single-crystal TriCS diffractometer (Paul ScherrerInstitute Switzerland 120582 = 118 A 120596-scan mode)

TheX-ray diffraction analysis (XRD) ofCNGS-2microre-gion sim03 times 03 times 03mm was carried out on a CAD-4 four-circle diffractometer at room temperature (MoK

120572radiation

graphite monochromator 120596-scan mode)

The crystal structure (atomic coordinates occupancies ofall positions) was refined using the full-matrix least squaresprocedure in the anisotropic approximation for all atomswithSHELXL-97 program package [25]

3 Results and Discussions

In the Ca3NbGa

3Si2O14structure each atom is located in the

individual position Ca in the dodecahedral (position 3e)Nb in the octahedral (position 1a) Ga in the tetrahedral(position 3f ) and Si in a trigonal-pyramidal (position 2d)[8] While in the La

3(Ga05Nb05)(1)Ga

3(2)Ga

2(3)O14crystals

lanthanum atoms are in the dodecahedral position of thestructure and gallium atoms occupy octahedral (Ga Nb)(1)position half replaced by the niobium atoms tetrahedralGa(2) and trigonal-pyramidal Ga(3) ones [17]

31 Ca3NbGa

3Si2O14

Crystals According to the neutrondiffraction data obtained (Table 1) CNGS-1 cut from the col-orless crystal has a composition (Ca

295◻

005(1))NbGa

3Si2O14

with vacancies (◻) located in the Ca position-119881ca10158401015840 The

deficiency of other positions as well as their occupation bythe other atoms (antistructural defects) was not detectedDue to the fact that the electroneutrality condition for therefined composition is not satisfied we assumed that a certainnumber of Ca2+ ions in the structure are interstitial onesas for the (La

2964◻

0036)Lai(0036)Zr05Ga5Si05O14 [26] The

analysis of the residual nuclear density does not excludesuch possibility The peak with the coordinates 119909 = 0464119910 = 0069 and 119911 = 0136 close to the interstitial Lai atomcoordinates (119909 = 0418 119910 = 0009 and 119911 = 0139) [26] wasfound Interstitial Cai atoms (like Lai atoms) are displacedfrom the dodecahedral positions approaching one of fouroxygen atoms thus forming two reduced CandashO (sim 206 A)and two increased distances According to Bokiy [27] ldquotheapparent size of the interstitial atomsdepends on their relativequantity the smaller relative quantity of dissolved non-metalthe smaller the apparent size of its atomsrdquo

Thereby it allow us to rewrite the CNGS-1 crystal compo-sition as (Ca

295◻

005(1))Cai(005)NbGa3Si2O14

Refining the structure of CNGS-2 cut from the yellowcrystal by direct methods allows revealing both atomiccoordinates similar to CNGS-1 ones (the unit cell 1) andatomic coordinates associated with the previous ones by thetransition matrix 10001000z+05 (the unit cell 2) Boththese unit cells are present in structure of CNGS-2 crystalin the ratio of unit cell 1 unit cell 2sim4 1 (Table 2) For thestructure determination the atomic coordinates of CNGS-1were taken as the initial ones However as a result of thecalculation fairly strong peaks of the residual nuclear densitywere foundThe coordinates of peaks correspond to a crystalmodel with a shift 12 zThe refinement of the structure usingthe second model (the initial coordinates are shifted by 12along the z-axis) based on electron density maps led to theappearance of strong peaks of the residual nuclear densitywith the coordinates of the initialmodel (without shift)Theseexperimental results suggest the existence of the translationtwin (like racemic twins) at the level of elementary cells In


(a) (b)


(a) (b)




3(Si1985◻

0015(10))(O1397(3)◻

003) (1198771= 523) with


∙∙)positions







3Si2O14and La


(NDA)


CNGS-1 80911 (2)49811 (1)

(Ca295◻

005(1))NbGa

3Si2O14

119877 = 415

LGN-1 82283 (4)51268 (3)

(La2935(2)◻

0065)(Ga0450

Nb0550(3)

)Ga3(Ga1965(4)◻

0035)(O1390(1)◻

010)

119877 = 810

LGN-2 82293 (3)51272 (2)

(La2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)

119877 = 724


CNGS-2Parameter


Ca 119910 05724 05936119911 0 05119909 0 0

Nb 119910 0 0119911 0 05119909 0 0

Ga 119910 02334 02501119911 05 0119909 13 13

Si 119910 23 23119911 04710 09700119909 13 13

O(1) 119910 23 23119911 01853 07245119909 01352 01553

O(2) 119910 04529 04489119911 03069 07638119909 02255 02553

O(3) 119910 01566 01511119911 02404 07638


3Si2O14



3Si2O14



3Si2O14



32 La3Ga55Nb05O14


3Ga55Nb05O14


2935(2)◻

0065)(Ga0450

Nb0550(3)

) Ga3

(Ga1965(4)◻

0035)(O1390(1)◻






2940(2)◻

0060)(Ga0485

Nb0515(6)

)(Ga2940(2)◻

0060)Ga2

(O1384(1)◻





2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)





3Ga55Nb05O14

crystal



3(GaTa5+)Ga

5O119910


n∙ ne1015840)times119881On∙gt (119881O


n∙lt (119881O


4 Conclusions


3Si2O14


3(Ga05Nb05)Ga5O14





3Ga55Nb05O14


3Ga55Nb05O14




3Si2O14and La



3Si2O14



3(Ga05Ta05)Ga5O14

and La3Ga4(GaSi)O

14crystals

References


3Ga5SiO14







3Ga5SiO14











3XY3Z2O14(A = Ca Sr




3NbGa

3Si2O14



3NbGa

3Si2O14








erties of Ca3NbGa

3Si2O14



















3NbGa

3Si2O14


















3NbGa










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


(a) (b)




3(Si1985◻

0015(10))(O1397(3)◻

003) (1198771= 523) with


∙∙)positions







3Si2O14and La


(NDA)


CNGS-1 80911 (2)49811 (1)

(Ca295◻

005(1))NbGa

3Si2O14

119877 = 415

LGN-1 82283 (4)51268 (3)

(La2935(2)◻

0065)(Ga0450

Nb0550(3)

)Ga3(Ga1965(4)◻

0035)(O1390(1)◻

010)

119877 = 810

LGN-2 82293 (3)51272 (2)

(La2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)

119877 = 724


CNGS-2Parameter


Ca 119910 05724 05936119911 0 05119909 0 0

Nb 119910 0 0119911 0 05119909 0 0

Ga 119910 02334 02501119911 05 0119909 13 13

Si 119910 23 23119911 04710 09700119909 13 13

O(1) 119910 23 23119911 01853 07245119909 01352 01553

O(2) 119910 04529 04489119911 03069 07638119909 02255 02553

O(3) 119910 01566 01511119911 02404 07638


3Si2O14



3Si2O14



3Si2O14



32 La3Ga55Nb05O14


3Ga55Nb05O14


2935(2)◻

0065)(Ga0450

Nb0550(3)

) Ga3

(Ga1965(4)◻

0035)(O1390(1)◻






2940(2)◻

0060)(Ga0485

Nb0515(6)

)(Ga2940(2)◻

0060)Ga2

(O1384(1)◻





2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)





3Ga55Nb05O14

crystal



3(GaTa5+)Ga

5O119910


n∙ ne1015840)times119881On∙gt (119881O


n∙lt (119881O


4 Conclusions


3Si2O14


3(Ga05Nb05)Ga5O14





3Ga55Nb05O14


3Ga55Nb05O14




3Si2O14and La



3Si2O14



3(Ga05Ta05)Ga5O14

and La3Ga4(GaSi)O

14crystals

References


3Ga5SiO14







3Ga5SiO14











3XY3Z2O14(A = Ca Sr




3NbGa

3Si2O14



3NbGa

3Si2O14








erties of Ca3NbGa

3Si2O14



















3NbGa

3Si2O14


















3NbGa










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





3Si2O14and La


(NDA)


CNGS-1 80911 (2)49811 (1)

(Ca295◻

005(1))NbGa

3Si2O14

119877 = 415

LGN-1 82283 (4)51268 (3)

(La2935(2)◻

0065)(Ga0450

Nb0550(3)

)Ga3(Ga1965(4)◻

0035)(O1390(1)◻

010)

119877 = 810

LGN-2 82293 (3)51272 (2)

(La2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)

119877 = 724


CNGS-2Parameter


Ca 119910 05724 05936119911 0 05119909 0 0

Nb 119910 0 0119911 0 05119909 0 0

Ga 119910 02334 02501119911 05 0119909 13 13

Si 119910 23 23119911 04710 09700119909 13 13

O(1) 119910 23 23119911 01853 07245119909 01352 01553

O(2) 119910 04529 04489119911 03069 07638119909 02255 02553

O(3) 119910 01566 01511119911 02404 07638


3Si2O14



3Si2O14



3Si2O14



32 La3Ga55Nb05O14


3Ga55Nb05O14


2935(2)◻

0065)(Ga0450

Nb0550(3)

) Ga3

(Ga1965(4)◻

0035)(O1390(1)◻






2940(2)◻

0060)(Ga0485

Nb0515(6)

)(Ga2940(2)◻

0060)Ga2

(O1384(1)◻





2940(1)◻

0060)(Ga0590

Nb0410(2)

)Ga5(O1382(1)◻

018)





3Ga55Nb05O14

crystal



3(GaTa5+)Ga

5O119910


n∙ ne1015840)times119881On∙gt (119881O


n∙lt (119881O


4 Conclusions


3Si2O14


3(Ga05Nb05)Ga5O14





3Ga55Nb05O14


3Ga55Nb05O14




3Si2O14and La



3Si2O14



3(Ga05Ta05)Ga5O14

and La3Ga4(GaSi)O

14crystals

References


3Ga5SiO14







3Ga5SiO14











3XY3Z2O14(A = Ca Sr




3NbGa

3Si2O14



3NbGa

3Si2O14








erties of Ca3NbGa

3Si2O14



















3NbGa

3Si2O14


















3NbGa










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





3(GaTa5+)Ga

5O119910


n∙ ne1015840)times119881On∙gt (119881O


n∙lt (119881O


4 Conclusions


3Si2O14


3(Ga05Nb05)Ga5O14





3Ga55Nb05O14


3Ga55Nb05O14




3Si2O14and La



3Si2O14



3(Ga05Ta05)Ga5O14

and La3Ga4(GaSi)O

14crystals

References


3Ga5SiO14







3Ga5SiO14











3XY3Z2O14(A = Ca Sr




3NbGa

3Si2O14



3NbGa

3Si2O14








erties of Ca3NbGa

3Si2O14



















3NbGa

3Si2O14


















3NbGa










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







3NbGa

3Si2O14


















3NbGa










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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