Thermal expansion of sintered polycrystals of hexacelsian solid solution (Sr, Ba) Al2Si2O8

The purpose of this work is to clarify the thermal expansion properties of hexacelsian solid solutions (SrxBa1-xAl2Si2O8, x = 0-1.0) using high-temperature powder X-ray diffraction and dilatometry of sintered polycrystals. Hexacelsian solid solutions were prepared from BaCO3, SrCO3 and finely purified kaolin powder (Al2O3 center dot 2SiO(2)center dot 2H(2)O) by heat-treatment above 1000 degrees C. Hexacelsian polycrystals showed more sluggish alpha-beta phase transitions, and the transition temperature increased from 300 to 700 degrees C with the increase in Sr content. The average thermal expansion coefficient of hexacelsian polycrystals strongly depended on the temperature range and on the Sr content because of their nonlinearity of expansion curves. The thermal expansion gap of the unit cell associated with the alpha-beta hexacelsian phase transition was found to increase from 0.13 to 0.50% with the increase in Sr content by high-temperature powder X-ray diffraction. The average linear thermal expansion coefficients of the alpha-hexacelsian and beta-hexacelsian unit cells showed nearly constant values of 6 x 10(-6)/K, though the expansion anisotropy of the crystal axes in unit cell altered depending on the chemical composition. (C) 2016 The Ceramic Society of Japan. All rights reserved.