Crystal Structure and Phase Transitions in Sr₃WO₆

Abstract

The crystal structures of the beta and gamma polymorphs of Sr(3)WO(6) and the gamma<-->beta phase transition have been investigated using electron diffraction, synchrotron X-ray powder diffraction, and neutron powder diffraction. The gamma-Sr(3)WO(6) polymorph is stable above T(c) approximately 470 K and adopts a monoclinically distorted double perovskite A(2)BB'O(6) = Sr(2)SrWO(6) structure (space group Cc, a = 10.2363(1)A, b = 17.9007(1)A, c = 11.9717(1)A, beta = 125.585(1)(o) at T = 1373 K, Z = 12, corresponding to a = a(p) + 1/2b(p) - 1/2c(p), b = 3/2b(p) + 3/2c(p), c = -b(p) + c(p), a(p),b(p), c(p), lattice vectors of the parent Fm3m double perovskite structure). Upon cooling it undergoes a continuous phase transition into the triclinically distorted beta-Sr(3)WO(6) phase (space group C1, a = 10.09497(3)A, b = 17.64748(5)A, c = 11.81400(3)A, alpha = 89.5470(2)(o), beta = 125.4529(2)(o), gamma = 90.2889(2)(o) at T = 300 K). Both crystal structures of Sr(3)WO(6) belong to a family of double perovskites with broken corner sharing connectivity of the octahedral framework. A remarkable feature of the gamma-Sr(3)WO(6) structure is a non-cooperative rotation of the WO(6) octahedra. One third of the WO(6) octahedra are rotated by approximately 45 degrees about either the b(p) or the c(p) axis of the parent double perovskite structure. As a result, the WO(6) octahedra do not share corners but instead share edges with the coordination polyhedra of the Sr cations at the B positions increasing their coordination number from 6 to 7 or 8. The crystal structure of the beta-phase is very close to the structure of the gamma-phase; decreasing symmetry upon the gamma-->beta transformation occurs because of unequal octahedral rotation angles about the b(p) and c(p) axes and increasing distortions of the WO(6) octahedra.

Subsolidus phase relations of the SrO–WO3–CuO system at 800°C in air

“…In the SrO-WO 3 -CuO phase diagram, three perovskite-related phases with compositions WO 3 (3−x)SrO xCuO (x = 1, 1/3 and 0) are found: Sr 2 CuWO 6 [24,55,56], Sr 8 CuW 3 O 18 (present work) and Sr 3 WO 6 [46]. Sr 2 CuWO 6 , is a double perovskite with an ordered distribution of Cu and W on the B-sites (P3).…”

“…According to the first study, SrWO 4 (tetragonal, space group I4 1 /a [45]) and Sr 3 WO 6 (monoclinic, space group Cc [46]) phases are the only binary oxide phases present in the system at 800 • C [43], an additional phase (Sr 2 WO 5 orthorhombic, space group Pmnb [47]) was found to be stable at this temperature in the second study [44].…”

“…Sr 3 WO 6 (Sr 2 SrWO 6 ) is an example of perovskite materials with Sr on both A-and Bsites. Sr 3 WO 6 has several polymorphs depending on temperature, and is an example of a double perovskite with broken corner sharing connectivity of the octahedral framework [46], resulting in an increase of the coordination around the Sr B-cations from 6 to 7 and 8. This is a result of a large difference in ionic radii of the B-site atoms (0.58Å) and low tolerance factor, t (0.89).…”

Synthesis, Characterization and Luminescence Properties οf Sr3WO6:Eu3+Phosphor

“…As is known, Sr 3 WO 6 has a double perovskite structure [11]. The positions of diffraction peaks (see in Fig.…”

Perovskite‐type Solid Solution SrMo1–xWx(O, N)3 Oxynitrides: Synthesis, Structure, and Magnetic Properties

“…Furthermore, double perovskite (for instance as for Sr 3 WO 6 , i.e. A 2 BB ′O 6 , with A , B :Sr and B ′:W) can be derived from the AB O 3 perovskite structure due to the large difference in ionic radius between Sr 2+ and W 6+ (ΔIR = 0.58 Å),31 where corner sharing connectivity is not maintained anymore.…”