Phase‐structure evolution and electrocaloric effect in Sr2NaNb4.3Ta0.7O15‐based filled tungsten bronze ceramics

Abstract To investigate the effect of A‐site substitution on phase‐structure evolution and electrocaloric effect (ECE) in filled tungsten bronze ceramics, Sr 2–3 x /2 La x NaNb 4.3 Ta 0.7 O 15 ( x = 0, 0.02, 0.04, and 0.06) ceramics are prepared through a two‐step solid‐state reaction method. Rietveld refinement shows that La 2 O 3 addition achieves a partial transition from orthorhombic ( Im 2 a ) to tetragonal phase ( P 4 bm ). A decrease in phase transition temperature, enhancement in distortion degree, and relaxation behavior are observed with increasing La 2 O 3 content, as demonstrated by dielectric, in situ Raman spectra, and ferroelectric properties. The indirectly measured ECE shows a non‐monotonic variation, with room‐temperature ECE ranging from 0.19, 0.15, 0.23 to finally 0.19 K for x = 0, 0.02, 0.04, and 0.06 compositions, respectively. This evolution trend is explained by an interplay of relaxation and multiphase coexistence. Directly measured ECE is also performed and a positive ECE character with a good temperature stability is observed. This work not only establishes relationships between phase‐structure evolution and ECE in filled Sr 2 NaNb 4.3 Ta 0.7 O 15 tungsten bronze ceramics, but also presents its possibility in applications of thermally stable EC devices.