High electrocaloric effect ferroelectric ceramics

Abstract

Abstract Effective ferroelectric ceramics of niobium-doped titanate-zirconate lead stannate of a high electrocaloric effect T = 2.6 K have been produced and studied. Production technology of lead scandium-tantalate PbSc.5Ta.5O3 (PST) ceramic solid solutions with operating temperature 260–295 K and maximum ΔT = 1.4–1.8 K at 20–30 kV/cm field amplitudes has been developed to use as active elements of cascade microcryogenic devices. Ceramic plates 10×15×0.5 mm cut from hot-pressed and annealed large-size blocks were used as samples and covered with fired silver paste electrodes. Density of ceramics from hydrostatic weight was found to be 97.2 to 97.4% of its theoretical value 9.071 g/cm3. The average grain-size was 3–4 μm. The large electrocaloric effect in PST as shown by precision X-ray experiments is due to the features of structure rearrangement at the cubic (Pm3m) to rhombohedral (R3m) phase transition (a large volume jump ΔV = +.0781 Å) and a high degree of scandium and tantalum ion ordering (ω = .85–.90–as determined from superstructure reflection intensities). A thermodynamic analysis of field and temperature effects on electrocaloric phenomena in PST solid solution ferroelectric ceramics has been made to vary position of the electrocaloric effect maximum vs. temperature by NB→TA and Ti → Ta, Sc substitution, its value being maintained at a high level of ΔT > 1 K. Introduction of niobium favors the grain growth while a simultaneous decrease of antiphase domains is observed: 120 nm in the case of pure PST and 30 nm for solid solution 0.6 PST-0.4 PSN. Substitutions in lead sublattice (Ba,Sr,Ca) or Zr,Hf→Ta,Sc result in a considerable “diffusion'’ of the electrocaloric effect vs. temperature curve and a drop of ΔT value.