Ionic transport and structural investigations on MSn(OH)6 (M = Ba, Ca, Mg, Co, Zn, Fe, Mn) hydroxide perovskites synthesized by wet sonochemical methods

Hydroxide perovskites of MSn(OH)6 (M = Ba, Ca, Mg, Co, Zn, Fe or Mn) were synthesized by co-precipitation and sonochemical reaction routes. Some of the compounds were also prepared by the hydrothermal method. These were characterized by XRD, TGA/DTA, TEM and IR studies. The hydroxide perovskites are stable up to ∼523 K and all the compounds stabilize in cubic crystal system (SG = Pn3m) at 298–523 K except BaSn(OH)6. The as-prepared powders of the above compositions show cubic square net in the reciprocal lattice of their electron diffraction patterns. Among these perovskites; MgSn(OH)6 and CoSn(OH)6 exhibit proton conduction at 298–500 K. Above ∼523 K, solid solutions of SnO2 and the corresponding MO components were observed. On heat-treatment at 850–950 K, M2−x(VM)xSnO4 (M-deficient spinel, x ≤ 1) along with SnO2 are observed. On further sintering to 1773 K for a duration of 6–7 h, M2−x(VM)xSnO4 phase is stabilized. The electrical properties of these compounds were measured by four-probe dc method. Co2−x(VCo)xSnO4 + SnO2 mixed phase showed oxide ion conductivity at 500–1273 K. The activation energy of oxide ion conduction is 0.93 eV. CaSn(OH)6does not show any type of electrical conduction at 298–850 K. The loss of proton conduction above 523 K may be ascribed to dehydroxylation and subsequent decomposition to SnO2 + M2−xSnO4 (defect spinel, M = Mg, Zn, Co) or MSnO3 (M = Ba, Ca).