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)