|
内容記述 |
Lead-free ferroelectric materials have attracted considerable attention as environmentally friendly alternatives to conventional lead-based systems such as Pb(Zr,Ti)O3. Among them, the perovskite-type solid solution (1-x)Bi0.5Na0.5TiO3–xBaTiO3 (BNT-BT) is a promising candidate due to its ferrielectricity [1] and high piezoelectric properties near the morphotropic phase boundary composition [2]. In our recent work, we found that the ferroelectric phase transition behavior of BNT-BT differs significantly between bulk ceramics and their ceramic powder form. To clarify the origin of this difference, we investigated the structural changes associated with the phase transition. BNT-BT ceramic pellets with BT-rich compositions were prepared using the solid-state reaction method. Bulk ceramic samples were cut into rods from the pellets, polished, and annealed. The remaining pellets were mechanically ground to prepare ceramic powder samples. Synchrotron radiation X-ray diffraction experiments were carried out at beamlines BL13XU and BL22XU in SPring-8, and the temperature dependence of the diffraction patterns for both the bulk ceramics and ceramic powder samples was investigated during the heating and cooling process. The bulk ceramics exhibited a sharp discontinuous phase transition from tetragonal to cubic symmetry, with clear thermal hysteresis, characteristic of a first-order phase transition. In contrast, the powder samples displayed a broader transition at a higher phase transition temperature. Furthermore, BL22XU data combined with the Rietveld analysis revealed the coexistence of tetragonal and cubic phases even at high temperature. Ferroelectrics are known to exhibit a pinning effect due to strain introduced by the aerosol deposition [3] and mechanochemical solid-state reaction [4]. In this study, we discuss how mechanical grinding of BNT–BT increases the phase transition temperature and explore the possible relationship to such pinning effects. |
