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

[摘要] Oxides of the type Ba_{3â€�?�ð�?��?}Sr_ð‘�?MgNb₂O₉ were synthesized by the solid state route. The ð‘�? = 0 composition (Ba₃MgNb₂O₉) was found to crystallize in a disordered (cubic) perovskite structure when sintered at 1000C. For higher Sr doping (ð‘�? â‰�? 0.5), there was clearly the presence of an ordered hexagonal phase indicated by the growth of superstructure reflections in the powder X-ray diffraction patterns. In all the compositions there was the presence of a minor amount of Ba_{5â€�?�ð�?��?}Sr_ð‘�?Nb₄O₁₅ phase which increased with Sr substitution up to ð‘�? = 1 and then it remained nearly constant at about 5%. Samples sintered at 1300C showed the hexagonally ordered phase for the entire range of composition (0 â‰�? ð‘�? â‰�? 3). The degree of ordering being considerably greater than in the 1000C heated samples as evidenced by several superstructure reflections.

[学科分类] 材料工程

[关键词] Oxides;X-ray diffraction;ordering;dielectric materials.