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in press
ACL
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B.Zheng, R.Ji, C.Genevois, W.Zhang, X.Ming, Q.Zhang, M.Allix, C.Yin, X.Kuang, X.Xing, 'Pressure-induced cation and vacancy disorder-order transition and near-zero τf in deficient hexagonal perovskite Ba8ZnTa6O24 dielectrics', Science China Chemistry (in press) doi:10.1007/s11426-024-2566-3
Pressure applications can enable the tuning of atomic/defect ordering and provide access to new functional materials. Here, we report that pressure-induced structural transformation featuring disorder-order transition of both cations and vacancies in the 8-layer deficient hexagonal perovskite tantalate dielectrics Ba8ZnTa6O24, which transformed the structure from twin to shift and remarkably lowered the temperature coefficient of resonant frequency τf down to near zero (∼0.56 ppm/°C) from 38 ppm/°C for the twinned precursor. The atomic scale STEM-HAADF and EDS results confirm the ordering of Zn in the Ta host at the nanometer scale in the shifted material featuring well-ordered Ba8ZnTa6O24 slabs intergrown with Ba3ZnTa2O9 and Ba5Ta4O15 monolayers and anti-phase grain boundaries as planar defects. The pressure-induced twin-shift structural transformation of Ba8ZnTa6O24 features the rare constant concentration of the hexagonal stacked layers, which is allowed by the vacancy ordering at the central layers of face-shared octahedral (FSO) trimers avoiding the FSO B-B repulsion, and remarkably the faster cationic ordering kinetics compared with the 2:1 ordered complex perovskites. Although the inclusion of numerous planar defects and the oxidizable atomic defects led to significant p-type conduction and inhomogeneous electrical microstructures, resulting in an extraordinarily high extrinsic dielectric loss for the high-pressure shifted Ba8ZnTa6O24 pellet, the intrinsically near-zero τf could make the shifted Ba8ZnTa6O24 perovskite an ideal microwave dielectric resonator candidate if the defects could be eliminated.
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