Tailoring the electromechanical properties of a material without altering the original composition is an emerging phenomenon for the optimization of functional properties. Post-sintering annealing with varying maximum temperatures, cooling rates, and atmospheres can influence the crystallographic phases, domain structures, conductivity, mechanical properties, and the temperature stability of the electromechanical properties. K_1/2Bi_1/2TiO₃ (KBT) is a high-temperature stable >280 °C A-site complex perovskite piezoelectric and is critical for high-temperature applications. However, the influence of annealing conditions on crystal structure, domain structure, and functional properties is not well-known. This work demonstrates the effect of annealing cooling rate and maximum temperature on the macroscopic electromechanical response as well as the crystal and domain structure. It is shown that the room-temperature state of KBT can be reversibly switched between the ferroelectric and relaxor state, where the slow cooling from 900 °C favors the stabilization of the relaxor state and quenching induces the ferroelectric state. Importantly, the quenched sample showed a stable piezoelectric coefficient up to 368 °C in the depolarization temperature, an increase of 78 °C. The origin of ferroelectric-relaxor state change is proposed to be related to the A-site cation redistribution and the associated change in the crystal structure and domain structure.

The direct conversion of methane to methanol using oxygen is a challenging but potentially rewarding pathway towards utilizing methane. By using a stepwise chemical looping approach, copper-exchanged zeolites can convert methane to methanol, but productivity is still too low for viable implementation. However, if the nature of the active site could be elucidated, that information could be used to design more effective catalysts. By employing anomalous X-ray powder diffraction with support from theory and other X-ray techniques, we have derived a quantitative and spatial description of the highly selective, active copper sites in zeolite omega (Cu-omega). This is the first comprehensive description of the structure of non-copper-oxo active species and will provide a pivotal model for future development for materials for methane to methanol conversion.