In this work, the thermal square wave method at single-frequency (TSWM) was applied to functionally graded BaTi 1−x Sn x O 3 samples with a tin gradient of 0.075≤x≤0.15. The samples were fabricated by sintering of bi-, tri-and tetramorph green bodies. The polarization at the back side with a higher tin content was in opposite direction to the polarization of the surface with a lower tin content. This was attributed to the appearance of a space charge layer. The determined depth profiles of the pyroelectric coefficient illustrate the appearance of a nearly constant polarization in the region of lower tin concentration of tri-and tetramorph samples. The pyroelectric coefficient profiles were in good agreement with the averaged over sample thickness pyroelectric coefficient obtained separately by the quasistatic method.
A gradient of the piezoelectric properties in monolithic ceramics can be useful to minimize mechanical stresses inside piezoelectric bending actuators or at interfaces between layers with different electromechanical properties, and increase the bandwidth of ultrasonic transducers. Piezoelectric gradients can be prepared by different techniques. We use a powder pressing technique to prepare a gradient of the chemical composition, which is transformed to the piezoelectric gradient by the poling process. Conventional mixed-oxide powders of BaTiO 3 with different amount of Sn from 7.5 up to 15 mol% and Mn-doped BaTiO 3 were used to produce lead-free ceramic samples. We describe the poling process using a equivalent circuit approach. The ferroelectric behavior of the different layers are described by the Preisach model. In the Ba(Ti,Sn)O 3 system the properties can be changed from ferroelectric to paraelectric depending on the Sn content. A gradient of polarization and piezoelectric properties can be observed in monolithic ceramics with a tin gradient. The profile of the polarization distribution was measured by the thermal wave method. A gradient of polarization where the sign of polarization changes can be induced in a system consisting of piezoelectric hard and soft materials. We describe a special poling process using our poling model. The principle is demonstrated in a two layer model system.
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