In order to investigate the effect of Mn on the dielectric and piezoelectric properties of PMN-PT [Pb(Mg 1 / 3 Nb 2 / 3)O 3-PbTiO 3 ], four different types of 71PMN-29PT samples were prepared using the solid-state single crystal growth (SSCG) method: (1) Undoped single crystals, (2) undoped polycrystalline ceramics, (3) Mn-doped single crystals, and (4) Mn-doped polycrystalline ceramics. In the case of single crystals, the addition of 0.5 mol% Mn to PMN-PT decreased the dielectric constant (K 3 T), piezoelectric charge constant (d 3 3), and dielectric loss (tan δ) by about 50%, but increased the coercive electric field (E C) by 50% and the electromechanical quality factor (Q m) by 500%, respectively. The addition of Mn to PMN-PT induced an internal bias electric field (E I) and thus specimens changed from piezoelectrically soft-type to piezoelectrically hard-type. This Mn effect was more significant in single crystals than in ceramics. These results demonstrate that Mn-doped 71PMN-29PT single crystals, because they are piezoelectrically hard and simultaneously have high piezoelectric and electromechanical properties, have great potential for application in fields of SONAR transducers, high intensity focused ultrasound (HIFU), and ultrasonic motors.

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In order to investigate the effect of thickness on the dielectric and piezoelectric properties of (001) PMN-29PT single crystals, three different types of PMN-29PT samples were prepared using the solid-state single crystal growth (SSCG) method: high density crystal [99%], low density crystal [95%], and high density crystal doped with Mn [98.5%]. When their thickness decreased from 0.5 mm to 0.05 mm, their dielectric constant (K 3 T), piezoelectric constants (d 3 3 and g 3 3), and electromechanical coupling factor (k t) decreased continuously. However, their dielectric loss (tan δ) increased. The addition of Mn to PMN-PT induced an internal bias electric field (E I), increased the coercive electric field (E C), and prevented local depoling. Therefore, Mn-doped PMN-PT crystals show high stability as well as high performance, even in the form of very thin plates (< 0.2 mm), and thus are suitable for application to high frequency composites, medical ultrasound probes, non-destructive testing devices (NDT), and flexible devices.

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