Synthesis of Water Sensing BaTi0.2Hf0.2Zr0.2Y0.2Nb0.2O3 Complex Oxide with High-Entropy B-site Configuration

A barium-based perovskite structured ceramic with five different B-site cations was prepared by a solid-state synthesis method. The phase and chemical homogeneity of the synthesised material was verified using x-ray diffraction and energy dispersive x-ray spectroscopy, showing the successful synthesis of a single-phase perovskite structure with Ba A-site and Ti, Hf, Zr, Y, Nb, B-site cations. Ultra-high vacuum x-ray photoelectron spectroscopy was used to reveal the valence states of the constituent elements. Conventional, two-step and spark plasma sintering were used to form dense pellets with limited grain growth. The room temperature electrical characteristics of the sintered pellets were investigated by electrochemical impedance spectroscopy where a conductivity increase of two orders of magnitude was observed in a water-bearing atmosphere. Synchrotron-based ambient-pressure x-ray photoelectron spectroscopy performed under water-bearing and dry conditions suggest that the conductivity increase is related to the incorporation of hydroxyl groups into the perovskite structure.