Calorimetric study of high pressure polymorphism in FeTiO3: Stability of the perovskite phase
Calorimetric study of high pressure polymorphism in FeTiO3: Stability of the perovskite phase
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DOI：
10.1007/bf00202133
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发表时间：
1994-08
影响因子：
1.4
通讯作者：
A. Mehta;K. Leinenweber;A. Navrotsky;M. Akaogi
中科院分区：
文献类型：
--
作者：
A. Mehta;K. Leinenweber;A. Navrotsky;M. Akaogi
量热法研究的钛铁矿和钛酸锂多晶型的FeTiO 3进行评估这些阶段的高压稳定性。钛铁矿是已知的在环境压力下的稳定相，但锂铁酸盐的形式可能是一个淬灭相从钙钛矿的形式，这是以前在原位观察到在highpressure.In这项研究中，锂铁TiO 3相合成钛铁矿起始材料在15- 16 GPa和1473 K，使用单轴裂球高压装置（USSA 2000）。采用转置温度降量热法研究了钛铁矿向钛酸锂转变的热力学。通过将样品在氩气中从环境条件下降到自发发生转化的温度来测量锂碳酸盐到钛铁矿的逆转化的热。在977 K下制成的液滴中，遇到了中间X射线非晶相。在1273 K，转换完成。用金刚石压砧法测量了钛铁矿向钛酸锂相变的体积变化，结果表明，钛铁矿向钛酸锂相变的体积变化与压力几乎无关，为-0.34cm ~3/mol。沿着转变的体积变化和先前公布的相平衡数据表明，钛铁矿至锂酸盐相边界相对于钛铁矿至钙钛矿相边界是亚稳的，并且高压下的稳定相可能是钙钛矿相。
A calorimetric study of the ilmenite and lithium niobate polymorphs of FeTiO3was undertaken to assess the high-pressure stabilities of these phases. Ilmenite is known to be the stable phase at ambient pressure, but the lithium niobate form may be a quench phase from a perovskite form which has been previously observed in situ at high pressure.In this study, the lithium niobate phase of FeTiO3was synthesized from an ilmenite starting material at 15– 16 GPa and 1473 K, using a uniaxial split-sphere high-pressure apparatus (USSA 2000). The energetics of the ilmenite to lithium niobate transformation were investigated through transposed-temperature drop calorimetry. The heat of back-transformation of lithium niobate to ilmenite was measured by dropping the sample in argon from ambient conditions to a temperature where the transformation occurs spontaneously. In drops made at 977 K, an intermediate x-ray amorphous phase was encountered. At 1273 K, the transformation went to completion. A value of -13.5±1.2 kJ/mol was obtained for the heat of transformation.A diamond anvil cell compression measurement on the lithium niobate phase was also performed, and indicated that the volume change for the ilmenite to lithium niobate transition is nearly pressure-independent, at-0.34cm3/mol.Thermodynamic calculations using the enthalpy of the ilmenite to lithium niobate transition, along with the volume change for the transition and previously published phase equilibrium data, indicate that the ilmenite to lithium niobate phase boundary is metastable with respect to an ilmenite to perovskite phase boundary, and the stable phase at high pressure is probably the perovskite phase.