The lutetium tantalate compounds obtained from Lu2O3–Ta2O5 with a molar ratio of 0.515 ： 0.485 were studied by Raman scattering and x-ray diffraction. The results of the room temperature Raman scattering indicate th...The lutetium tantalate compounds obtained from Lu2O3–Ta2O5 with a molar ratio of 0.515 ： 0.485 were studied by Raman scattering and x-ray diffraction. The results of the room temperature Raman scattering indicate that the sample has a phase transition between 1830℃ and 1872℃, the polycrystalline is a mixture of M-LuTaO4 and Lu3TaO7（F m3m）when it is prepared at 1830℃, and a mixture of M-LuTaO4（B112/b） and Lu3 Ta O7（Fm3^-m） when it is prepared at above 1872℃. The sample melts at a temperature of 2050℃. The phase transition of the sample prepared at 2050℃ was also investigated by the high-temperature Raman spectra, and the result indicates that no phase transition occurs between room temperature and 1400℃, which is consistent with the results from the x-ray diffraction.展开更多
Nearly all displacive transitions have been considered to be continuous or second order, and the rigid unit mode （RUM） provides a natural candidate for the soft mode. However, in-situ X-ray diffraction and Raman mea...Nearly all displacive transitions have been considered to be continuous or second order, and the rigid unit mode （RUM） provides a natural candidate for the soft mode. However, in-situ X-ray diffraction and Raman measurements show clearly the first-order evidences for the scheelite-to-fergusonite displacive transition in SaWO4： a 1.6% volume collapse, coexistence of phases, and hysteresis on release of pressure. Such first-order signatures are found to be the same as the soft modes in BaWO4, which indicates the scheelite-to-fergusonite displacive phase transition hides a deeper physical mechanism. By the refinement of atomic displacement parameters, we further show that the first-order character of this phase transition stems from a coupling of large compression of soft BaOs polyhedrons to the small displacive distortion of rigid WO4 tetrahedrons. Such a coupling will lead to a deeper physical insight in the phase transition of the common scheelite-structured compounds.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51172236,51272254,51102239,and 61205173)the National Science Fund for Distinguished Young Scholars,China(Grant No.61405206)
文摘The lutetium tantalate compounds obtained from Lu2O3–Ta2O5 with a molar ratio of 0.515 ： 0.485 were studied by Raman scattering and x-ray diffraction. The results of the room temperature Raman scattering indicate that the sample has a phase transition between 1830℃ and 1872℃, the polycrystalline is a mixture of M-LuTaO4 and Lu3TaO7（F m3m）when it is prepared at 1830℃, and a mixture of M-LuTaO4（B112/b） and Lu3 Ta O7（Fm3^-m） when it is prepared at above 1872℃. The sample melts at a temperature of 2050℃. The phase transition of the sample prepared at 2050℃ was also investigated by the high-temperature Raman spectra, and the result indicates that no phase transition occurs between room temperature and 1400℃, which is consistent with the results from the x-ray diffraction.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11179030 and 90714011)the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KJCX2-SW-N20)
文摘Nearly all displacive transitions have been considered to be continuous or second order, and the rigid unit mode （RUM） provides a natural candidate for the soft mode. However, in-situ X-ray diffraction and Raman measurements show clearly the first-order evidences for the scheelite-to-fergusonite displacive transition in SaWO4： a 1.6% volume collapse, coexistence of phases, and hysteresis on release of pressure. Such first-order signatures are found to be the same as the soft modes in BaWO4, which indicates the scheelite-to-fergusonite displacive phase transition hides a deeper physical mechanism. By the refinement of atomic displacement parameters, we further show that the first-order character of this phase transition stems from a coupling of large compression of soft BaOs polyhedrons to the small displacive distortion of rigid WO4 tetrahedrons. Such a coupling will lead to a deeper physical insight in the phase transition of the common scheelite-structured compounds.
