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Zachary Neale

MSE 473

Glass Project I

Titanate Glass

Titanate refers to any chemical composition consisting of titanium oxides. The most

common type of titanate, titanium(IV) oxide (TiO2), is used mostly for pigments in paints,

toothpaste, paper, and plastics [1]. In glass, TiO2can be used as a modifier or as a glass former.

However, it has been observed that TiO2cannot form a glass by itself and must be combined

with a glass modifier such as Cs2O or BaO [2].

The coordination state and structure of titanate as a glass former has been the focus of

research especially during the 1980s. The most common naturally occuring crystal structure of

TiO2is the rutile crystal structure. Titanium has a six-fold coordination with oxygen in the rutile

structure forming an oxygen octahedral. This violates Zachariasens second rule of glass

forming oxides that the coordination number of the cation should be 3 or 4. In addition,

Zachariasens first rule that oxygen may not be linked to more than two cations is also in

violation as shown in equation 1.

Although TiO2fails Zachariasens first two rules, the ionic ratio of Ti4+

to O2-

at 0.43 is

close to belonging to coordination 4 which is below 0.414. This is similar to the ionic ratio of

Alumina which is an intermediate glass former. In addition, the field strength of both four-fold

and six-fold coordinated Ti-O classifies it as an intermediate glass former as described in

equation (2-5).

()

()

(2)

(3)

()

()

(4)

(5)

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Many studies have attempted to characterize the atomic structure of TiO2in binary glass

systems using various techniques. In 1980 a research group from Washington State University

in collaboration with the Boeing Company, General Electric Company, and Corning Glass

Works studied the coordination of Ti in the TiO2-SiO2binary system using extended x-ray

absorption fine structure technique [3]. Testing samples with a titania composition less than

10%, the study found that the titanium oxide formed mostly four-fold tetrahedral sites.

Increasing the concentration of TiO2decreased the amount of tetrahedra and increased six-fold

coordinate octahedral sites as seen by the absorption spectra in figure 1.

The peak illustrated by the graph represents the four-fold coordination Ti-O bond for 9.5% TiO3.

Levels a and b are the same peak intensities for 3.4% and 7.5%. From this study it is concluded

that TiO2as a glass modifier predominantly takes on a coordination number of 4 in a binary glass

system with SiO2. Also, as the concentration of TiO2increases, the amount of octahedralcompared to tetrahedral increases as shown by the decreasing in peak intensity.

Furthermore, in 1986 a study was performed on the formation of high TiO 2content BaO

containing glass using TiO2as the only glass network former [4]. This study used infrared

absorption spectroscopy to identify the coordination number of Ti4+

in high concentration glass

systems. It found the IR peak associated with the six-fold coordinated Ti-O bond shown in

Figure 1. Near-edge X-ray absorption spectra for 9.5% TiO2in SiO2.

Tetrahedral

Ti-O bond

a: 3.4%

b: 7.5%

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figure 2 by comparing it with the stretching mode of the Ti-O bond in BaTiO3crystal which is

also in an octahedral coordination.

It was found that most of the TiO2 had coordination number 6 and made octahedral. The amount

of octahedra did not change much from 30-50% TiO2. It was postulated that this structure of

titanate glass consisted of a three-dimensional network of corner sharing TiO6octahedra.

In contrast to this study, it was found in 1989 that if the binary system consisted of an

alkali metal oxide (M2O) that the TiO2would switch to predominantly four-fold coordination [5].

This study used Raman spectra to measure Ti-O coordination between different alkali metal

oxide and titania binary glass systems. The study compared the Raman peaks to that of titanate

crystals with various coordination numbers. It made use of the Ba2TiO4crystal which is one of

the only titanate crystals known to have a four-fold coordination number of Ti4+

. The study

concluded that the TiO2glass system was primarily made of Ti

4+

ions in tetrahedra with a smallquantity of octahedra, unlike the previous study. The difference is the use of the alkali metal

oxide modifier. In addition, the study found that the amount of octahedra decreased with

increasing alkalinity as seen by the decrease in octahedra peak intensity in figure 3.

Figure 2.

Ti-O

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Summary

Although TiO2violates two of Zachariasens rules for being a glass, it can be seen as a

glass modifier and a glass network former in two different structures. While the TiO2

concentration is under 10% it acts as a modifier and has mostly tetrahedral coordination. As the

percentage of TiO2 increases in a non-alkali glass the number of Ti4+

with coordination number 6

increases. It was found that if an alkali metal oxide is used to modify the titanate glass, the Ti4+

Tetrahedra

Octahedra

Figure 2. Raman spectra of alkali titanate glasses.

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cations form tetrahedral with coordination number 4. Furthermore, increasing the alkalinity of

the modifier increases the ratio of tetrahedra to octahedra.

Works Cited

[1] Ceret sana, "Market Study: Titanium Dioxide," 2013.

[2] S. Sakka, "Structures of gallate, aluminate and titanate glasses,"Journal of Non-Crystalline Solids, vol.

123, no. 1-3, pp. 176-181, 1990.

[3] D. R. Sandstrom, "Coordination of Ti in TiO2-SiO2 Glass by X-Ray Absorption Spectroscopy,"Journal

of Non-Crystalline Solids, vol. 41, pp. 201-207, 1980.

[4] C. Jijian, "FORMATION AND STRUCTURE OF TITANATE GLASSES,"Journal of Non-Crystalline Solids,

vol. 80, pp. 135-140, 1986.

[5] S. Sakka, "STRUCTURE OF BINARY K20-TiO 2 AND Cs20-TiO 2 GLASSES,"Journal of Non-Crystalline

Solids, vol. 112, pp. 64-68, 1989.

[6] R. D. Shannon, "Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in

Halides and Chalcogenides,"Acta Crystallographica, vol. A32, pp. 751-767, 1976.