High-entropy ceramics have been gaining attention over the last 20 years due to their ability to combine the favourable properties of their constituent elements. Entropy effects stabilize a simple crystal structure with near equal amounts of 5 or more component elements distributed homogeneously throughout the lattice. These materials have shown increased thermal and environmental stability and interesting electrical and dielectric and catalytic properties. In this study we produced a Barium Titanate based ceramic with a cubic structure and investigated its electrical properties.
BaCO3, TiO2, ZrO2, HfO2, Y2O3 and Nb2O5 were combined with the cationic ratio 1:0.2:0.2:0.2:0.2:0.2 of Ba:Ti:Zr:Hf:Y:Nb [MK1] before being high-energy ball milled for 5 hours. The resulting mixture was dried and calcined to produce a compositionally homogenous single-phase powder verified by x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX). We produced dense BaTi0.2­Hf0.2Zr0.2Y0.2Nb0.2O3 by conventional sintering at 1300 °C and 1500 °C, two- step sintering at with a first step temperature of 1500 °C and second step of 1300 °C, and spark plasma sintering with a range of grain sizes.
The impedance characteristics were measured using a Probostat system with Solatron 1260 impedance analyser at room temperature in atmospheres of air, O2, H2,  and N2 with 4300, 8,600 and 17,000 ppm H2O and Au/Pd electrodes. A fast, reversible change in the capacitance of over 2 orders of magnitude in 800 seconds was observed when water was introduced to the atmosphere.
In-situ X-ray photoelectron spectroscopy (XPS) was performed on the In Situ Spectroscopy Beamline at the Paul Scherrer Institute, Switzerland. High-resolution core-level scans were performed at 850 eV and 1100 eV under an N2 and an N2 + H2O atmosphere. Peak envelope components corresponding to lattice oxygen in the BaTiO3 structure and oxygen in the O-H bonding environment could be identified. The percentage area of the peak envelope corresponding to lattice bound oxygen was seen to decease in the scans performed in a wet atmosphere whilst the area corresponding to oxygen in O-H groups increased from 40 – 90% of the peak area. We conclude these changes are due to an increase in the OH concentration in the crystal lattice and attribute the increased conductivity to these defects.