Piezoelectric and pyroelectric properties of calcium-modified and grain-oriented (NaBi)1/2Bi4Ti4O15ceramics

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Abstract
Grain orientation effects of (NaBi)(l-x)/2Ca x Bi4Ti4O15 (NCBT-100x) ceramics, which belong to a bismuth layer-structured ferroelectric (BLSF) family, are studied using the hot-forging (H.F.) method on the piezoelectric and pyroelectric properties. The dielectric constant ε s is small and almost constant at the wide range of composition (x = 0tox = 1). The Curie temperature, Tc , increases as the Ca concentration increases. The grain orientation (H.F.) effects enhance the piezo- and pyroelectric properties by a factor of two or more if compared with non-oriented ones. The H.F. and Mn-doped NCBT-5 ceramics, with a lower free permittivity ε33 T/ε0 (= ∼ 130) and higher electromechanical coupling factor k 33 (= 33 ∼ 40%), along with a higher anisotropy k 33/k 31 (= 13 ∼ 17), are very attractive candidate materials for hydrophone applications at high temperatures or for high-frequency ultrasonic transducers. Pyroelectric properties are also very interesting for sensor materials, and the figure of merit (Fv ) is comparable to that of PZ-based or PT-based materials.