Synthesis of Cubic Cs-deficient Pollucite and its Low Thermal Expansion Property

抄録

Pollucite compounds, Cs_1-XAl_1-XSi_2+XO₆ (X=0.0, 0.1, 0.2, 0.25) with cubic symmetry at 298 K, were synthesized by multi-step heat treatment. The synthesized CsAlSi₂O₆ and Cs_0.9Al_0.9Si_2.1O₆ were tetragonal below 223 K and 173 K, respectively, while the synthesized Cs_0.8Al_0.8Si_2.2O₆ and Cs_0.75Al_0.75Si_2.25O₆ were cubic even at 123 K. Cubic Cs_0.75Al_0.75Si_2.25O₆ showed low thermal expansion in the temperature range of 123 to 1173 K, of which the mean linear thermal expansion coefficient in the range of 123 to 1173 K was 1.47×10^-6 K^-1. From the relationship between the thermal expansion properties and lattice volumes of the synthesized pollucite compounds, it was considered that the low thermal expansion properties of Cs_0.8Al_0.8Si_2.2O₆ and Cs_0.75Al_0.75Si_2.25O₆ were due to smaller distortion of the aluminosilicate framework compared to Cs_1-XAl_1-XSi_2+XO₆ (X=0.0, 0.1), and that the formation of space around Cs sites in the unit cells resulted in the cubic structure at 123 K for Cs_1-XAl_1-XSi_2+XO₆ (X=0.2, 0.25).