Electrocaloric effect at special points in the composition-temperature-electric field phase diagram of barium zirconate-titanate (BZT)

The composition-temperature-electric field diagram and electrocaloric properties of BaTi1_xZrxO3 (BZT) were computed using a self-consistent phenomenological approach. By subtracting contributions from the latent heat, the adiabatic temperature change due solely to the material polarization was quantified on passing through critical end, tricritical and phase convergence points. The largest temperature change occurs at the first-order paraelectric to ferroelectric transitions where the latent heat is triggered, but the material polarization contri-bution is greatest at the critical temperature. The maximum electrocaloric responsivity occurs at a field 1.25 times greater than the critical field. The temperature change increases at the tricritical point due to a field -induced tetragonal to rhombohedral transformation, but the responsivity diverges due to vanishing of the crit-ical field. The enhanced temperature change observed experimentally near the convergence point is attributed to greater polarization change in the rhombohedral phase, and to a polar glasslike state that contributes to the dipolar configurational entropy.

Automated summary

The composition-temperature-electric field diagram and electrocaloric properties of BaTi1_xZrxO3 (BZT) were calculated. The adiabatic temperature change due to material polarization at critical end, tricritical, and phase convergence points was quantified. The largest temperature change occurred at the first-order paraelectric to ferroelectric transitions, while the greatest material polarization contribution was observed at the critical temperature. The maximum electrocaloric responsivity occurred at a field 1.25 times greater than the critical field. The enhanced temperature change near the convergence point was attributed to greater polarization change in the rhombohedral phase and a polar glasslike state that contributed to the dipolar configurational entropy.