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The highly anisotropic electrocaloric effect, evidenced by both direct measurements and a descriptive theoretical model in lead‐free relaxor ferroelectric Sr0.75Ba0.25Nb2O6 single crystals, can be exploited by producing low‐cost grain‐oriented ceramics. Combined with the broad‐temperature‐range cooling regime provided by their polar nanoregions, these materials may be the key to future cost‐ and energy‐efficient solid‐state refrigeration.

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The ferroelectric phase transition of uniaxial Ca 0.28 Ba 0.72 Nb 2 O 6 single crystals with a moderate effective charge disorder was investigated by Brillouin scattering to clarify the dynamic properties. In the tetragonal paraelectric phase a remarkable softening of the sound velocity of the longitudinal acoustic mode and a significant increase in the sound attenuation were observed close to the Curie temperature T C = 527 K. The intermediate temperature T * ∼ 640 K and the Burns temperature T B ∼ 790 K were determined from the temperature variation in the sound attenuation. The intense broad central peak (CP) caused by polarization and strain fluctuations due to polar nanoregions was clearly observed in the vicinity of T C . The relaxation time determined by the CP width clearly shows critical slowing down towards T C , reflecting a weakly first-order phase transition under weak random fields.