Synthesis of zirconium titanate with an ordered M-fergusonite (beta) structure

We report a new zirconium titanate compound (Zr,Ti)O2 with 27.5–35 mol% titania (TiO2) formed from the oxides at 35–38 kbar, 1400–1500 °C. Crystal structure investigations at atmospheric conditions with powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed a monoclinic structure related to that of M-fergusonite (beta). Unit-cell dimensions (from 27.5 to 35 mol% TiO2): a=7.267(20)–7.340(2) Å, b=10.435(3)–10.429(1) Å, c=5.023(11)–5.040(1) Å, β=136.45(12)–137.55(1)°, V=262.44(92)–260.40(12) Å3, Z=4. Rietveld refinement (RF=1.55) of a sample with 32.8 mol% TiO2 indicates that site A is 8-fold coordinated, mostly occupied by Zr, while site B has 6-fold average coordination, occupied by Ti and Zr. Site B is at least partly ordered, as indicated by superstructure reflections 0 0 1 and −2 0 1 detected with TEM, reducing the space group from C2/c to C2. Pronounced streaking of selected diffraction spots is linked to the boundaries of lamellar domains in twin orientation, with twin planes either (200) or (20−2). Adjacent lamellae differ slightly in composition, causing subtle asymmetry of the twin diffraction patterns.