A low/intermediate-temperature entropy-stabilized tengerite (LITES-T) as a stable high-k dielectric with hydration-activated ionic transport

High-permittivity dielectrics and low-temperature ionic conductors are essential for sensing and energy technologies, but their stability and processability at intermediate temperatures remain limited. Here, we report an entropy-stabilized, tengerite-structured high-entropy rare-earth carbonate (SLYNT) that can be densified by cold sintering at 200 °C without decomposition and exhibits a stable high-k dielectric response. In the dry state, SLYNT shows a near-ideal capacitive phase angle from 1 kHz to 1 MHz, an effective permittivity of about 103, and a sub-percent temperature coefficient between 25 and 200 °C. Upon hydration, a reversible low-frequency resistive branch emerges while the high-frequency permittivity is retained, leading to an apparent ionic conductivity of 10-3–10-4 S cm-1 from room temperature to 200 °C with an activation energy of about 0.22 eV. These findings identify entropy-stabilized tengerite carbonates as promising hydration-gated reconfigurable electroceramics for stable high-capacitance-density and hydration- activated ion transport.