Majtyka-Piłat, Anna; Chrobak, Dariusz; Nowak, Roman ... · Based on structural data collected in...

This is an electronic reprint of the original articleThis reprint may differ from the original in pagination and typographic detail

Powered by TCPDF (wwwtcpdforg)

This material is protected by copyright and other intellectual property rights and duplication or sale of all or part of any of the repository collections is not permitted except that material may be duplicated by you for your research use or educational purposes in electronic or print form You must obtain permission for any other use Electronic or print copies may not be offered whether for sale or otherwise to anyone who is not an authorised user

Majtyka-Piłat Anna Chrobak Dariusz Nowak Roman Wojtyniak Marcin Dulski MateuszKusz Joachim Deniszczyk JoacutezefStructural and Electronic Properties of Qatranaite

Published inAdvances in Materials Science and Engineering

DOI10115520194031823

Published 22042019

Document VersionPublishers PDF also known as Version of record

Please cite the original versionMajtyka-Piat A Chrobak D Nowak R Wojtyniak M Dulski M Kusz J amp Deniszczyk J (2019) Structuraland Electronic Properties of Qatranaite Advances in Materials Science and Engineering 2019 [4031823]httpsdoiorg10115520194031823

Research ArticleStructural and Electronic Properties of Qatranaite

Anna Majtyka-Piłat 1 Dariusz Chrobak1 Roman Nowak 2 Marcin Wojtyniak 3

Mateusz Dulski1 Joachim Kusz3 and Jozef Deniszczyk1

1Institute of Materials Science University of Silesia in Katowice 75 Pułku Piechoty 1A 41-500 Chorzow Poland2Nordic Hysitron Laboratory Department of Materials Science and Engineering Aalto University 00076 Espoo Finland3Institute of Physics University of Silesia Uniwersytecka 4 40-007 Katowice Poland

Correspondence should be addressed to Roman Nowak romannowakaaltofi

Received 10 December 2018 Revised 6 March 2019 Accepted 19 March 2019 Published 22 April 2019

Academic Editor Joon-Hyung Lee

Copyright copy 2019 Anna Majtyka-Piłat et al 0is is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

0e present work addresses the atomic structure and electronic properties of a recently discovered mineral qatranaite(CaZn2(OH)6middot2H2O) 0e present study was performed theoretically by means of density functional theory- (DFT-) basedcalculations within the frame of local density approximation (LDA) and general gradient approximation (GGA) To determine theenergy band gap width we carried out the ultraviolet-visible spectroscopy (UV-Vis) measurements 0e structure relaxationperformed with use of LDA and GGA provides results matching the experimentally determined crystal parameters Interestinglyin contrast to existing interpretation of experimental data our DFT calculations revealed energy gap of direct characteristicsAccordingly our UV-Vis experiments yield the band gap width of 39 eV

1 Introduction

Qatranaite named after the village Al Qatrana (situated15 km southeast from the Amman Aquaba Asia-JordanDesert Highway) is considered as a natural analogue ofsynthetic calcium hexahydroxodizincate dehydrate [1 2]0e mineral discovered in an altered pyrometamorphicspurrite rocks in the Daba-Siwaqa region of the Hatrurimcomplex located in Jordan [3ndash6] was for the first timedescribed in 2016 by Stasiak et al as CaZn2(OH)6middotOH2O [7]Qatranaite crystallized in the temperature range 150 to200degC similarly as Se-bearing thaumasite or afwillite in theform of flatten (010) crystals growing up to 03mm [7 8]

Qatranaite unit cell consists of octahedrally coordinatedCa2+ ions linked to four hydroxy groups and two water mol-ecules whereas Zn2+ ions are tetrahedrally coordinated withfour OHminus groups and form pyroxene-like chains [Zn2(OH)6]2minus0e mineral may display charge deficiency in case all oxygenatoms participate in the formation of OH groups which cer-tainly affects electronic properties of this interestingmaterial [8]

0e potential application of calcium hexahydrox-odizincate dehydrate-like systems sparked hope for

improved chargedischarge reversibility in Zn batteryelectrodes Furthermore they are expected to restrict Zn-electrode shape change and inhibit dendrite formation[1 2 9ndash11] Additionally electrochemical properties ofCaZn2(OH)6middot2H2O make it suitable for negative electrodesin rechargeable zinc-air batteries [12 13]

0e energy gap of calcium hexahydroxodizincatedehydrate has been a subject of experimental in-vestigations [2] from which the direct energy gap width of31 eV has been concluded Our UV-Vis measurements ofqatranaite revealed that the spectrum can be equally wellinterpreted assuming the presence of direct or indirectenergy gap In order to disclose the nature of the energygap in the mineral we carried out the quantum DFT-based electronic structure investigations by means ofthe pseudopotential method employed in the QuantumEspresso package [14] To verify reliability of the calcu-lations we have also performed the structural optimi-zation and compared the results with experimental dataAn ab initio prediction for the energy band gap wascompared with experimental results provided by UV-Vismeasurements

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 4031823 6 pageshttpsdoiorg10115520194031823

2 Computational and Experimental Details

An ab initio calculations were carried out using theQuantum Espresso code [14] by applying the scalar rela-tivistic ultrasoft pseudopotentials [15] for Ca(3s23p64s2)H(1s2) and O(2s22p6) elements within both LDA and GGAcalculations For Zn we used the same type pseudopotentialswith (3d974s24p03) and (3d104s2) valence state configurationfor LDA and GGA respectively Calculations were per-formed for two approximations of exchange correlation(XC) energy functional 0e LDA XC functional in the formparameterized by Perdew and Zunger [16] and the GGA XCfunctional proposed by Perdew et al [17] were employed0e plane wave kinetic energy and charge density cutoff of46 and 368 Ry respectively were applied within LDA whilein the case of GGA the corresponding cutoff values equaled53 and 368 Ry 0e structure-optimization following theBroydenndashFletcherndashGoldfarb-Shanno (BFGS) scheme wascarried out within LDA and GGA approaches 0e usage ofthe 12times12times12 MonkhorstndashPack mesh [18] in reciprocalspace enabled us to achieve satisfactory convergence in thestructural optimization 0e total energy of the qatranaiteunit cell was evaluated with an accuracy of 5meV whileforces were calculated with uncertainty less than 008 and521meVA for LDA and GGA respectively To determineprecisely the details of electronic density of states the ad-ditional calculations using the 20times 20times 20 MonkhorstndashPackmesh were performed

To study the energy gap of qatranaite the ultraviolet-visible spectroscopy (UV-Vis) was performed with the use ofmicrospectrophotometer (CRAIC Technologies) equippedwith standard halogen lamp and Zeiss 15x objective 0esample was prepared in the form of petrographic polishedplate with the qatranaite crystals (diameter of 03mm)embedded in the mineral matrix 0e experiments wereperformed at room temperature and ambient pressure Toestimate the band gap width we use the formula proposed byWood and Tauc [19]

h] middot α sim h]minusEg1113872 1113873n (1)

where α is the absorbance h stands for the Planck constant ]defines the photonrsquos frequency Eg denotes the optical bandgap energy and n is a constant related to different kinds ofelectronic transitions 0e n parameter equals 05 2 15 and3 for direct indirect allowed and forbidden transitionsrespectively

3 Results and Discussion

31 Structural Properties According to the experimentalresults provided by Stasiak et al [7] the CaZn2(OH)6middot2H2Omineral crystallizes in the P21c-type structure with the fol-lowing lattice parameters a 63889(8) A b 10969(1) Ac 57588(8) A and β 10195(1)deg 0e coordination of eachZn atom to four oxygen atoms and Ca atom to six oxygenatoms prompted the authors to imagine the qatranaite unitcell as a particular set of tetrahedral ZnO4 and octahedralCaO6 clusters (Figure 1) Peculiarity of the qatranaite unit cellis related to the presence of hydroxyl groups [OH] attached to

hydrogen bridges to H2O molecules [20] which ensures theelectric charge balance

Tables 1 and 2 summarize the results of ab initiostructural optimization of qatranaite unit cell carried outwith the use of two approximations for XC energy func-tional 0e calculated results were compared with availableexperimental data It is worth emphasizing that the output ofDFT-LDA calculations is in well agreement with the pre-viously reported diffraction data [7 8] (Table 1) 0ecomputed (LDA) andmeasured a b c lattice parameters andβ angle differ less than 02 23 35 and 21 respectivelyGGA approach give slightly worse results (correspondingdifferences are 41 29 56 and 06) It can be concludedthat LDA XC functional better describes the nature ofbonding in qatranaite

In Table 2 we compare experimental and optimizedcoordinates of Wyckoff positions in the structure ofCaZn2(OH)6middot2H2O mineral To avoid the issue of highmobility of hydrogen atoms [21] their experimentally ob-tained coordinates were frozen during structural optimi-zation We are satisfied with the overall agreement betweencalculated and measured coordinates of Wyckoff positions[8] 0e noticeable difference in Wyckoff position can beobserved for oxygen atoms which may be attributed to theirrelative high mobility [22]

Figure 1 Schematic of the crystalline structure of qatranaiteshowing the tetrahedrally coordinated zinc (ZnO4 yellow) andoctahedrally coordinated calcium (CaO6 blue) clusters 0e red andgreen spheres denote oxygen and hydrogen atoms respectively

2 Advances in Materials Science and Engineering

Based on structural data collected in Table 2 we alsocalculated an interatomic distances in tetrahedral ZnO4 andoctahedral CaO6 clusters e obtained results are presentedin Table 3 e comparison of DFT structural results withexperimental data conrms sucient reliability of ourcalculations

32 Electronic Properties Physical properties of a novelmaterial are essential for its intended applications inelectronics and photonics Consequently the energy bandstructure and the details of qatranaitersquos partial density ofstates (PDOS) are of common interest Indeed our DFT-determined band diagram (Figure 2) indicates the in-sulating property of qatranaite with a direct band gap atthe Γ-point of reciprocal k-lattice of 32 eV (LDA) and33 eV (GGA)

Closer inspection of Figure 2 reveals that the selection ofLDA and GGA of exchange-correlation energy does notsignicantly aect the shape of energy bands Furthermorethe partial DOS analysis (Figure 3) reveals the electronicstates near the top of the valence-band lled by O-p and Zn-d electrons with slight contribution of Ca electrons

33 UV-Vis Absorption Spectroscopy e results obtainedfrom our DFT calculations demonstrated that qatranaite isthe direct band gap material and consequently the n valueof 05 have to be used in equation (1) e energy band gapEg 39 eV was estimated by tting equation (1) to theexperimental points at the linear portion of the curve(Figure 4) e latter value exceeds the one deduced fromDFT calculations (Eg 32 eV) is conrms the commonperception that DFT calculations frequently lead to

Table 1 Lattice parameters of qatranaite estimated with the LDA and GGA and compared with the measured values

Parameters LDA GGA Exp [7]a (A) 6388 6652 6389b (A) 10720 11286 10969c (A) 5960 6081 5759β (deg) 10405 10252 10195

Table 2 Experimental and calculated coordinates of Wycko positions in qatranaite single crystal

AtomExp [8] DFT-LDA DFT-GGA

X Y Z x Y z x y zZn1-4e 05332 06650 06639 05300 06670 06385 05313 06669 06536O1-4e 04687 06814 03122 04451 06933 03030 04540 06891 03108H1-4e 05227 061710 02675 mdash mdash mdash mdash mdash mdashO2-4e 03380 05427 07455 03557 05309 07117 03440 05363 07084H2-4e 03226 05543 08576 mdash mdash mdash mdash mdash mdashO3-4e 08349 06236 07394 08377 06388 06993 08311 06308 07010H3-4e 08739 06108 085960 mdash mdash mdash mdash mdash mdashO4-4e 00373 06603 02367 00206 06422 02193 00262 06486 02274H4-4e 01712 06704 02490 mdash mdash mdash mdash mdash mdashH5-4e minus001980 07304 02400 mdash mdash mdash mdash mdash mdashCa1-2a 00000 00000 00000 00000 00000 00000 00000 00000 00000For hydrogen atoms ldquomdashrdquo stands for experimental values of coordinates

Table 3 Interatomic distances in ZnO4 and CaO6 clusters

Interatomic distances (A)Zn1 Ca1

O1 O1 O2 O3 O2 O2 O3 O3 O4 O4LDA 196 194 195 193 234 234 229 230 230 229GGA 205 200 200 199 240 240 239 235 235 239Exp[7] 191 199 195 194 237 237 237 234 234 234

e atomic symbols (eg O1 and O2) denote atoms occupying dierentWycko positions

ZΓ Γ ΓD B E

GGA Eg = 33 eV LDA Eg = 32 eV

ndash2

0

2

4

6

8

Ener

gy (e

V)

Figure 2 e electronic band structure of crystalline qatranaitedetermined within LDA (green lines) and GGA (red lines) ezero of the energy scale is shifted to the top of the valence band

Advances in Materials Science and Engineering 3

underestimation of the band gap [23] 0erefore it may beconcluded that the true energy gap in qatranaite shouldsignificantly exceed the calculated DFT value

Finally the calculations and experimental results ob-tained for natural qatranaite were compared with previouslypublished data for synthetic counterpart [2] 0us Xavieret al measured the energy gap Eg of 31 eV the value sig-nificantly lower than the one obtained by our UV-Vis ab-sorption spectroscopy measurements Such a highdiscrepancy is due to disputable assumptions imposed byXavier et al [2] who fitted their absorption results in such away that stipulates n 2 (equation (1)) 0e differencesbetween experimentally derived energy gap for qatranaite(39 eV) and synthetic CaZn2(OH)6middot2H2O (31 eV) [2] maystem from chemical and structure imperfections present inmineral qatranaite

4 Conclusions

In sum we have demonstrated the DFT calculations withinLDA and GGA schemes accurately predict the atomicstructure which encourage the further study of qatranaiteelectronic properties0e calculated lattice parameters at theground state conditions are in agreement with the experi-mental results It is contend therefore that LDA is moreappropriate for estimation of lattice parameters of qatra-naite 0e LDA (GGA) predicted direct band gap energy at Γpoint of the first Brillouin zone provided the lower value32 eV (33 eV) compared to our experimentally obtained39 eV data Moreover it is worth noting that our theoreticaland experimental results reveal the presence of direct gap inqatranaite mineral where available experimental data for itssynthetic analogue pointed on indirect energy gap We

0

01

02

03

ndash4 ndash2 0 2 4 6

DO

S (s

tate

seV

)

Energy (eV)

LDA Ca-sLDA Ca-pGGA Ca-s

GGA Ca-pGGA Ca-d

(a)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA H-sGGA H-s

(b)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA O-sLDA O-p

GGA O-sGGA O-p

(c)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA Zn-sLDA Zn-pLDA Zn-d

GGA Zn-sGGA Zn-d

(d)

Figure 3 Partial density of states determined for qatranaite 0e zero of the energy scale is shifted to the top of the valence band


believe that the output of our calculations contains in-formation being of importance to the modern electronic andphotonic industries

Data Availability

e raw data from all implemented techniques (UV-VISDFT) used to support the ndings of this study are availablefrom the corresponding author upon request

Disclosure

e authors would like to inform that a small part of theirsimulation results were previously published in a posterform

Conflicts of Interest

e authors declare no consecticts of interest regarding thepublication of this paper

Acknowledgments

is research was partially supported by PL-Grid In-frastructure DCH acknowledges the support from theNational Science Centre of Poland (Grant no 201621BST802737)

References

[1] C-C Yang W-C Chien P-W Chen and C-Y WuldquoSynthesis and characterization of nano-sized calcium zincatepowder and its application to Ni-Zn batteriesrdquo Journal ofApplied Electrochemistry vol 39 no 1 pp 39ndash44 2009

[2] C S Xavier J C Sczancoski L S Cavalcante et al ldquoA newprocessing method of CaZn2(OH)6middot2H2O powders photo-luminescence and growth mechanismrdquo Solid State Sciencesvol 11 no 12 pp 2173ndash2179 2009

[3] Y Bentor ldquoIsraelrdquo in Lexique Stratigraphique InternationalAsie vol 3 p 80 Centre National de la Recherche Scienti-que Paris France 1960

[4] S Gross ldquoe mineralogy of the Hatairim formation IsraelrdquoGeological Survey of Israel Bulletin vol 70 pp 1ndash80 1977

[5] E Sokol I Novikov S Zateeva Y Vapnik R Shagam andO Kozmenko ldquoCombustion metamorphism in the NabiMusa dome new implications for a mud volcanic origin of theMottled Zone Dead Sea areardquo Basin Research vol 22 no 4pp 414ndash438 2010

[6] Y Vapnik V Sharygin E Sokol and R Shagam ldquoParalavas ina combustion metamorphic complex Hatrurim Basin IsraelrdquoGeological Society of America Reviews in Engineering Geologyvol 18 pp 1ndash21 2007

[7] M Stasiak E V Galuskin J Kusz et al ldquoIMA commission onnew minerals nomenclature and classication (CNMNC)Qatranaite IMA 2016-024rdquo Mineralogical Magazine vol 80no 32 pp 915ndash922 2016

[8] Y Vapnik E V Galuskin I O Galuskina et alldquoQatranaiteCaZn2(OH)6middot2H2Omdasha new mineral from alteredpyrometamorphic rocks of the Hatrurim Complex Daba-Siwaqa Jordan in reviewrdquo European Journal of Mineralogy2019

[9] R Stahl H Jacobs and Z Anorg ldquoZur kristallstruktur vonCaZn2(OH)6middot2H2Ordquo Zeitschrift fur anorganische und allge-meine Chemie vol 623 no 8 pp 1287ndash1289 1997

[10] X M Zhu H X Yang X P Ai J X Yu and Y L CaoldquoStructural and electrochemical characterization of mecha-nochemically synthesized calcium zincate as rechargeableanodic materialsrdquo Journal of Applied Electrochemistry vol 33no 7 pp 607ndash612 2003

[11] J Yu H Yang X Ai and X Zhu ldquoA study of calcium zincateas negative electrode materials for secondary batteriesrdquoJournal of Power Sources vol 103 no 1 pp 93ndash97 2001

[12] Y-J Min S-J Oh M-S Kim J-H Choi and S EomldquoCalcium zincate as an ecient reversible negative electrodematerial for rechargeable zincndashair batteriesrdquo Ionics vol 24pp 1ndash7 2018

[13] A RMainar E Iruin L C Colmenares et al ldquoAn overview ofprogress in electrolytes for secondary zinc-air batteries andother storage systems based on zincrdquo Journal of EnergyStorage vol 15 no 1 pp 304ndash328 2018

[14] P Giannozzi S Baroni N Bonini et al ldquoQUANTUMESPRESSO a modular and open-source software project forquantum simulations of materialsrdquo Journal of Physics Con-densed Matter vol 21 no 39 article 395502 2009

[15] httpwwwquantum-espressoorgpseudopotentialspslibrary[16] J P Perdew and A Zunger ldquoSelf-interaction correction to

density-functional approximations for many-electron sys-temsrdquo Physical Review B vol 23 no 10 pp 5048ndash50791981

[17] J P Perdew K Burke and M Ernzerhof ldquoGeneralizedgradient approximation made simplerdquo Physical Review Let-ters vol 77 no 18 pp 3865ndash3868 1996

[18] H J Monkhorst and J D Pack ldquoSpecial points for Brillouin-zone integrationsrdquo Physical Review B vol 13 no 12pp 5188ndash5192 1976

[19] D L Wood and J Tauc ldquoWeak absorption tails in amorphoussemiconductorsrdquo Physical Review B vol 5 no 8 pp 3144ndash3151 1972

[20] T-C Lin M Y A Mollah R K Vempati and D L CockeldquoSynthesis and characterization of calcium hydroxyzincateusing X-ray diraction FT-IR spectroscopy and scanning

25 30 35 40 45

0

1 times 1016

2 times 1016

Experimental dataLinear fit

(αhν

)2 (eV

cm

)2

Energy hν (eV)

Eg = 390 eV

Figure 4 UV-Vis spectrum of qatranaite (black dots) Linear taccording to equation (1) shows the energy gap width Eg


force microscopyrdquo Chemistry of Materials vol 7 no 10pp 1974ndash1978 1995

[21] D Gaspar L Pereira K Gehrke B Galler E Fortunato andR Martins ldquoHigh mobility hydrogenated zinc oxide thinfilmsrdquo Solar Energy Materials and Solar Cells vol 163pp 255ndash262 2017

[22] M Boccard N Rodkey and Z C Holman ldquoHigh-mobilityhydrogenated indium oxide without introducing water duringsputteringrdquo Energy Procedia vol 92 pp 297ndash303 2016

[23] J P Perdew R G Parr M Levy and J L Balduz ldquoDensity-functional theory for fractional particle number derivativediscontinuities of the energyrdquo Physical Review Letters vol 49no 23 pp 1691ndash1694 1982


CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018


Journal of

Chemistry

Analytical ChemistryInternational Journal of


ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of



Advances in Condensed Matter Physics


International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of


High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in



ChemistryAdvances in


Advances inPhysical Chemistry


BioMed Research InternationalMaterials

Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

Research ArticleStructural and Electronic Properties of Qatranaite

Anna Majtyka-Piłat 1 Dariusz Chrobak1 Roman Nowak 2 Marcin Wojtyniak 3

Mateusz Dulski1 Joachim Kusz3 and Jozef Deniszczyk1

1Institute of Materials Science University of Silesia in Katowice 75 Pułku Piechoty 1A 41-500 Chorzow Poland2Nordic Hysitron Laboratory Department of Materials Science and Engineering Aalto University 00076 Espoo Finland3Institute of Physics University of Silesia Uniwersytecka 4 40-007 Katowice Poland

Correspondence should be addressed to Roman Nowak romannowakaaltofi

Received 10 December 2018 Revised 6 March 2019 Accepted 19 March 2019 Published 22 April 2019

Academic Editor Joon-Hyung Lee

Copyright copy 2019 Anna Majtyka-Piłat et al 0is is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

0e present work addresses the atomic structure and electronic properties of a recently discovered mineral qatranaite(CaZn2(OH)6middot2H2O) 0e present study was performed theoretically by means of density functional theory- (DFT-) basedcalculations within the frame of local density approximation (LDA) and general gradient approximation (GGA) To determine theenergy band gap width we carried out the ultraviolet-visible spectroscopy (UV-Vis) measurements 0e structure relaxationperformed with use of LDA and GGA provides results matching the experimentally determined crystal parameters Interestinglyin contrast to existing interpretation of experimental data our DFT calculations revealed energy gap of direct characteristicsAccordingly our UV-Vis experiments yield the band gap width of 39 eV

1 Introduction

Qatranaite named after the village Al Qatrana (situated15 km southeast from the Amman Aquaba Asia-JordanDesert Highway) is considered as a natural analogue ofsynthetic calcium hexahydroxodizincate dehydrate [1 2]0e mineral discovered in an altered pyrometamorphicspurrite rocks in the Daba-Siwaqa region of the Hatrurimcomplex located in Jordan [3ndash6] was for the first timedescribed in 2016 by Stasiak et al as CaZn2(OH)6middotOH2O [7]Qatranaite crystallized in the temperature range 150 to200degC similarly as Se-bearing thaumasite or afwillite in theform of flatten (010) crystals growing up to 03mm [7 8]

Qatranaite unit cell consists of octahedrally coordinatedCa2+ ions linked to four hydroxy groups and two water mol-ecules whereas Zn2+ ions are tetrahedrally coordinated withfour OHminus groups and form pyroxene-like chains [Zn2(OH)6]2minus0e mineral may display charge deficiency in case all oxygenatoms participate in the formation of OH groups which cer-tainly affects electronic properties of this interestingmaterial [8]

0e potential application of calcium hexahydrox-odizincate dehydrate-like systems sparked hope for

improved chargedischarge reversibility in Zn batteryelectrodes Furthermore they are expected to restrict Zn-electrode shape change and inhibit dendrite formation[1 2 9ndash11] Additionally electrochemical properties ofCaZn2(OH)6middot2H2O make it suitable for negative electrodesin rechargeable zinc-air batteries [12 13]

0e energy gap of calcium hexahydroxodizincatedehydrate has been a subject of experimental in-vestigations [2] from which the direct energy gap width of31 eV has been concluded Our UV-Vis measurements ofqatranaite revealed that the spectrum can be equally wellinterpreted assuming the presence of direct or indirectenergy gap In order to disclose the nature of the energygap in the mineral we carried out the quantum DFT-based electronic structure investigations by means ofthe pseudopotential method employed in the QuantumEspresso package [14] To verify reliability of the calcu-lations we have also performed the structural optimi-zation and compared the results with experimental dataAn ab initio prediction for the energy band gap wascompared with experimental results provided by UV-Vismeasurements

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 4031823 6 pageshttpsdoiorg10115520194031823


























ZΓ Γ ΓD B E


ndash2

0

2

4

6

8

Ener

gy (e

V)





4 Conclusions


0

01

02

03


DO

S (s

tate

seV

)

Energy (eV)


GGA Ca-pGGA Ca-d

(a)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA H-sGGA H-s

(b)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA O-sLDA O-p

GGA O-sGGA O-p

(c)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)


GGA Zn-sGGA Zn-d

(d)




Data Availability


Disclosure




Acknowledgments


References





















25 30 35 40 45

0

1 times 1016

2 times 1016


(αhν

)2 (eV

cm

)2

Energy hν (eV)

Eg = 390 eV










Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





























ZΓ Γ ΓD B E


ndash2

0

2

4

6

8

Ener

gy (e

V)





4 Conclusions


0

01

02

03


DO

S (s

tate

seV

)

Energy (eV)


GGA Ca-pGGA Ca-d

(a)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA H-sGGA H-s

(b)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA O-sLDA O-p

GGA O-sGGA O-p

(c)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)


GGA Zn-sGGA Zn-d

(d)




Data Availability


Disclosure




Acknowledgments


References





















25 30 35 40 45

0

1 times 1016

2 times 1016


(αhν

)2 (eV

cm

)2

Energy hν (eV)

Eg = 390 eV










Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






4 Conclusions


0

01

02

03


DO

S (s

tate

seV

)

Energy (eV)


GGA Ca-pGGA Ca-d

(a)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA H-sGGA H-s

(b)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)

LDA O-sLDA O-p

GGA O-sGGA O-p

(c)

0

20

40

60

80


DO

S (s

tate

seV

)

Energy (eV)


GGA Zn-sGGA Zn-d

(d)




Data Availability


Disclosure




Acknowledgments


References





















25 30 35 40 45

0

1 times 1016

2 times 1016


(αhν

)2 (eV

cm

)2

Energy hν (eV)

Eg = 390 eV










Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





Data Availability


Disclosure




Acknowledgments


References





















25 30 35 40 45

0

1 times 1016

2 times 1016


(αhν

)2 (eV

cm

)2

Energy hν (eV)

Eg = 390 eV










Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls











Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




Majtyka-Piłat, Anna; Chrobak, Dariusz; Nowak, Roman ... · Based on structural data collected in...

Documents

Transcript of Majtyka-Piłat, Anna; Chrobak, Dariusz; Nowak, Roman ... · Based on structural data collected in...