Quasi-adiabatic calorimeter for direct electrocaloric measurements.

The electrocaloric effect (ECE) in ferroelectric materials is a promising candidate for small, effective, low cost, and environmentally friendly solid state cooling applications. Instead of the commonly used indirect estimates based on Maxwell's relations, direct measurements of the ECE are required to obtain reliable values. In this work, we report on a custom-made quasi-adiabatic calorimeter for direct ECE measurements. The ECE is measured for two promising lead-free materials: Ba(ZrTi)O and Ba(ZrTi)O bulk ceramics. Adiabatic temperature changes of ΔT = 0.5 K at 355 K and ΔT = 0.3 K at 314 K were achieved under the application of an electric field of 2 kV/mm for the Ba(ZrTi)O and Ba(ZrTi)O samples, respectively. The quasi-adiabatic ECE measurements reliably match other direct EC measurements using a differential scanning calorimeter or an infrared camera. The data are compared to indirect EC estimations based on Maxwell's relations and show that the indirect measurements typically underestimate the effect to a certain degree.