Thermal Expansion of MgTiO3 Made by Sol-Gel Technique at Temperature Range 25–890 °C

Abstract

MgTiO3 is a material commonly used in the industry as capacitors and resistors. The high-temperature structure of MgTiO3 has been reported only for materials synthesized by the solid-state method. This study deals with MgTiO3 formed at low temperatures by the sol-gel synthesis technique. Co-precipitated xerogel precursors of nanocrystalline magnesium titanates, with Mg:Ti ratio near 1:1, were subjected to thermal treatment at 1200 °C for 5 h in air. A sample with fine powders of MgTiO3 (geikielite) as a major phase with Mg2TiO4 (qandilite) as a minor phase was obtained. The powder was scanned on a hot-stage X-ray powder diffractometer at temperatures between 25 and 890 °C. The lattice parameters and the atomic positions of the two phases were determined as a function of temperature. The thermal expansion coefficients of the geikielite were derived and compared with previously published data using the solid-state synthesis technique, providing insights on trends in materials properties at elevated temperature as a function of synthesis. It was found that the deviation of the present results in comparison to previously reported data do not originate from the method of synthesis but rather from the fact that there is an asymmetric solubility gap in geikielite. The lattice parameters of this study present the property of stoichiometric MgTiO3 and are compared to previously reported non-stoichiometric MgTiO3 with excess of Ti. The values of lattice parameters of the non-stoichiometric versus temperature of geikielite found the same for both solid-state reaction and sol-gel products.

Thermodynamic properties of geikielite (MgTiO3) and ilmenite (FeTiO3) derived from vibrational methods combined with Raman and infrared spectroscopic data

“…2 shows that volume expansion is sensitive to the average Grüneisen parameter. In particular, the curve shows that the average value for the Grüneisen parameter, between 0.9 and 1.3, derived from the optic modes established by Raman spectroscopic measurements of Okada et al (2008) and Reynard and Guyot (1994) is too small to explain the volume expansion measured by Henderson (2009;Tuval et al 2020) and Zabicky et al 2009). These volume expansion data can only be explained by an average Grüneisen parameter of about 1.4.…”

“…based on a mixture of 95 wt% MgTiO 3 and 5 wt% Mg 2 TiO 4 (qandilite). According to Shindo (1980) and Wechsler and Navrotsky (1984), MgTiO 3 is a non-stoichiometric compound, which is able to dissolve a small excess quantity of Ti, but not Mg. Tuval et al (2020) showed experimentally and with the help of the phase diagram of MgO-TiO 2 published by Shindo (1980), that their sample contains MgTiO 3 near the stoichiometric composition, whereas the sample of Henderson et al (2009) most likely contains an excess of Ti, which explains the difference between the available V-T data sets. The V-T data set of Zabicky et al (2009) is consistent with that of Tuval et al (2020), because their sample is also a mixture of MgTiO 3 and Mg 2 TiO 4 .…”

“…Lower-right: The dot-dashed curve has been calculated with an average Grüneisen parameter for MgTiO 3 of 1.25. The dashed curve results from an optimization directed towards the data of Henderson et al (2009), who synthesized a sample that likely contains an excess Ti, whereas the solid curve results from an optimization directed towards the data of Tuval et al (2020) and Zabicky et al (2009). The vertical bars labelled 'T', 'L' and 'S' are volumes of ilmenites measured at ambient conditions (the bars are offset from 300 K).…”

“…Related to the findings above, some remarks on sample characterization of geikielite are appropriate here. Figure 2 shows that we have directed our optimization towards the V-T data of Tuval et al (2020) and Zabicky et al (2009). The V-T data sets of Henderson et al (2009) and those of Tuval et al (2020) are based on different samples.…”

“…Figure 2 shows that we have directed our optimization towards the V-T data of Tuval et al (2020) and Zabicky et al (2009). The V-T data sets of Henderson et al (2009) and those of Tuval et al (2020) are based on different samples. The data set of Henderson et al (2009) is based on a mixture of small amounts of TiO 2 (rutile) and MgTiO 3 , and a large amount of MgTi 2 O 5 (karrooite), whereas that of Tuval et al ( 2020) is ( 7)…”