| Research Abstract |
We chose a cubic pollucite, CsA1Si_2O_6, as a template compound, and report that the cubic Cs-leucite compounds with various chemical compositions can be synthesized by multi-step heating process as a solid-state reaction method, and that the thermal expansion properties in the range 298-1273K for all of the synthesized compounds were examined by using low- and high-temperature XRD.
The results obtained can be summarized as follows. 1. Cubic cesium leucite-based compounds, Cs_<1-x> Al_<1-x>Si_<2+x> O_6 (x=0.0-0.25), Cs_<1-x> Na_xAlSi_2O_6 (x=0.1-0.25), Cs_<0.9-x> Na_xAl_<0.9> Si_2O_6 (x=0.1-0.25), and Cs_<0.9-x> Li_xAl_<0.9> Si_<2.1> O_6 (x=0.1,0.2), were synthesized using multistep heat treatment. Their crystal structures were cubic, with space group Ia-3d, in the range of 298-1273K. 2. The variation in unit cell volume with temperature for each composition was showed that Cs_<0.8> Al_<0.8> Si_<2.2> O_6 and Cs_<0.75> Al_<0.75> Si_<2.25> O_6 had significantly smaller degrees of lattice
… More
thermal expansion than CsAlSi_2O_6 and Cs_<0.9> Al_<0.9> Si_<2.1> O_6 CsAlSi_2O_6, Cs_<0.9> Al_<0.9> Si_<2.1> O_6, Cs_<0.8> Al_<0.8> Si_<2.2> O_6 and Cs_<0.75> Al_<0.75> Si_<2.25> O_6 showed linear coefficients of thermal expansion of 2.7×10^<-6>, 2.2×10^<-6>, 1.5×10^<-6> and 1.1×10^<-6> K^<-1>, respectively, which are attributed to an increase in not only space ratio but also Al/Si ratio in the framework in the unit cell. 3. Structural phase transition was accompanied by a significant decrease in the Cs content of compounds of the Cs_<1-x> Al_<1-x> Si_<2+x> O_6 series. Cs_<0.8> AL_<0.8> Si_<2.2> O_6 and C_<s0.75> A_<l0.75> Si_<2.25> O_6 were cubic at 123 K from the XRD patterns and did not undergo structural phase transition. 4. Cesium sodium leucites and cesium lithium leucites showed a lower thermal expansion than that of cesium leucites. In particular, the thermal expansion of Cs_<0.7> Na_<0.2> Al_<0.9> Si_<2.1> O_6 decreased to 0.14% at 1273K and that of Cs_<0.7> Li_<0.2> Al_<0.9> Si_<2.1> O_6 decreased to 0.081% at 1273K. 5. The lattice thermal expansion behavior of the synthesized cubic (Cs,Na)-pollucite compounds was investigated by high-temperature XRD analysis in the temperature range of RT-1173 K and was found to show a gradual decrease with decreasing Cs content of Cs_<1-x> Na_xAlSi_2O_6 and Cs_<0.9-x> Na_xAl_<0.9> Si_<2.1>O_6 series. 6. The lattice thermal expansion behavior of the synthesized cubic (Cs,Na)-Leucite compounds, Cs_<1.0> Na_xAl_<1+x> Si_<2-x>O_6 and Cs_<1-x> Na_xAlSi_2O_6 (x=0.1,0.2,0.3) was found to attribute to not only Al/Si ratio in the framework but also arrengements of Cs^ + ion and Na^+ ion in the unit cell. Less
|
