HIGH SYMMETRY BRINGS HIGH Q INSTEAD OF ORDERING IN Ba(Zn_(1/3)Nb_(2/3)O_3 : A HRTEM STUDY

摘要

Ba(Zn_(1/3)Nb_(2/3)O_3 : (BZN), which exhibits a complex perovskite structure with an order-disorder transition at 1350 °C, has been examined in terms of ordering ratio and microstructure by the Rietveld method and by high resolution transmission electron microscopy (HRTEM), respectively. Two types of sample are used: sample A is a high temperature form sintered at 1400 °C for 100 h; sample B is a low temperature form, based on the high temperature form (sample A) which has been annealed at 1200 °C for 100 h. Ordering ratios of the two samples A and B are 27.6 and 54.2 %, respectively. By HRTEM observations, it was found that both samples exhibit disordered parts, without a superlattice, and ordered parts with a superlattice. This interpretation is supported by synchrotron XRPD data collected at Diamond in Oxford UK. Part of the ordering in sample A might have appeared during quenching. In the case of sample B, the ordering ratio was expected to be 80 % as shown for BZT in a previous paper.