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.
Highlights
The MgO-TiO2 ceramic system includes three stoichiometric magnesium titanate phases: Mg2 TiO4(qandilite), MgTiO3 and MgTi2 O5 [1]
Accurate thermal expansion coefficients were measured for sol-gel products of stoichiometric solubility range in the geikielite
The lattice parameters of MgTiO3 made by sol-gel synthesis measured in High-temperature X-ray diffraction (HT-XRD) between reaction (Kar2) measured by High-temperature neutron diffraction (HT-ND) were mixtures of geikielite and karrooite with maximum excess
Summary
(qandilite), MgTiO3 (geikielite) and MgTi2 O5 (karrooite) [1] Their crystal structures have been determined by X-ray diffraction and neutron diffraction [2,3]. Geikielite, MgTiO3 , is rhombohedral of ilmenite type, space group R-3 (148), Pearson Symbol hR10.0; formed at temperatures above 600 ◦ C, is stable from room temperature to its melting point; Qandilite, Mg2 TiO4 , cubic of inverse spinel type, space group Fd-3m (227), Pearson Symbol cF56.0, formed at above 1150 ◦ C; Karrooite, MgTi2 O5 , orthorhombic of pseudo-brookite type, space group Cmcm (63), Pearson. High-temperature X-ray diffraction (HT-XRD) studies have been published for all three stoichiometric Mg titanates prepared by the sol-gel technique during their transformation from the xerogel precursor to their final oxide form for a range of temperatures between 700 and 1300 ◦ C [4]. There was agreement between the lattice parameter of the HT-XRD and HT-ND data in the temperature range between
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