Structural crossover from long period modulated to non-modulated cubic-like phase at cryogenic temperature in the morphotropic phase boundary of Na_(0.5)Bi_(0.5)TiO_3-BaTiO_3

摘要

Morphotropic phase boundary (MPB) composition 0.94Na_(0.5)Bi_(0.5)TiO_3-0.06BaTiO_3 (NBT-6BT) has received industrial acceptance in certain aspects such as ultrasonic cleaners to replace those of lead-based systems. While detailed structure-property analysis on NBT-6BT is mostly confined to room temperature and above, less attention is paid with regard to their structure and property understanding below room temperature. In this work, utilizing the complementarity of Raman spectroscopy, x-ray diffraction, and neutron powder diffraction, we unravel low temperature polar-structural behavior of the MPB composition. While x-ray diffraction shows the persistence of a cubic like global structure in the temperature interval from 300 to 100 K, neutron diffraction reveals a structural crossover from long period modulated to non-modulated P4bm + R3c phase coexistence at ~150K. We show that the tendency of growing ferroelectric ordering with reducing temperature is responsible for the structural crossover. Concurrence of weak anomaly in dielectric loss (tan 8) at the same temperature seems to be correlated to the structural crossover.