Structures of Na0.74WO3.

摘要: The structures of the four phases exhibited by Na(0.74)WO(3), sodium tungstate, with a change in temperature have been refined from powder diffraction patterns obtained on high-resolution diffractometer (HRPD), ISIS, Rutherford Appleton Laboratory, England. At temperatures above 430 K, stable phase has ideal perovskite structure, space group Pm3;m (No. 221). Below that temperature, octahedra are tilted about pseudocubic directions; tilts produced condensation normal modes vibration high-temperature cubic phase. Using Glazer's notation, tilt system undergoes following sequence: a+a+a+ (293K)-->a+a+a0(343K)-->a0a0a+(430K)-->a0a0a0. structural refinements presented here confirm sequence transitions first proposed Clarke [(1977). Phys. Rev. Lett. 39, 1550-1553]. This is time structure determination a+a+a0 reported literature. In addition, we evaluate weights, or importance, condensed each low-temperature