Influence of strontium on the cubic to ordered hexagonal phase transformation in barium magnesium niobate

Oxides of the type Ba3-xSrxMgNb2O9 were synthesized by the solid state rout e. The x = 0 composition (Ba3MgNb2O9) was found to crystallize in a disorde red (cubic) perovskite structure when sintered at 1000C. For higher Sr dopi ng (x greater than or equal to 0.5), there was clearly the presence of an o rdered hexagonal phase indicated by the growth of superstructure reflection s in the powder X-ray diffraction patterns. In all the compositions there w as the presence of a minor amount of Ba5-xSrxNb4O15 phase which increased w ith Sr substitution up to x = 1 and then it remained nearly constant at abo ut 5%, Samples sintered at 1300C showed the hexagonally ordered phase for t he entire range of composition (0 less than or equal to x less than or equa l to 3 ). The degree of ordering being considerably greater than in the 100 0C heated samples as evidenced by several superstructure reflections.