Dielectric, thermal, electrocaloric, elastic, optical, and electromechanical properties of three ferroelectrics with diffuse phase transition (PLZT 8/65/35 ceramics, lead magnesium niobate and strontium barium niobate single crystals) me investigated in dependence on temperature and electric field strength. It is shown that a polar phase can be induced by a n electric field within the nonpolar phase and vice versa, depending on whether the temperature is above or below Tb < T , . Analogies to stress-induced martensic transformations are emphasized. Dielektrische, thermische, elektrokalorische, elastische, optische und elektromechanische Eigenschaften von drei Ferroelektrika mit diffuser Phasenumwandlung (PLZT 8/65/35-Keramik, Bleimagnesiumniobat-und Strontiumbariumniobat-Einkristalle) werden in Abhingigkeit von der Temperatur und der elektrischen Feldstarke untersucht. Es wird gezeigt, daB sich eine polare Phase durch ein elektrisches Feld innerhalb der unpolaren induzieren laDt und umgekehrt eine unpolare in einer polaren, je nachdem ob die Temperatur ober-oder unterhalb T t < TC liegt. Auf Analogien zu spannungsinduzierten martensitischen Transformationen wird hingewiesen.
SBN 75 and PLZT 8/65/35, two ferroelectrics with different structure and symmetry which exhibit diffused phase transition, show similar aging effects: a lessening of the dielectric losses and of the dielectric dispersion by lowering the low‐frequency dielectric constant (DC), a doubling of the hysteresis loop within the slim loop region, a lowering of the transition temperature Tt. and special features in the field dependence of the DC. The results are discussed in terms of the two‐level relaxation model proposed by Reinecke and Ngai.
The knowledge of the dielectric large signal properties of piezoelectric actuators for dynamic use is necessary to estimate the limits of application, to optimize the driving electronics, and to improve the actuator materials. A measurement technique has been developed for determination of the large signal parameters capacity, loss tangent, loss power, and dilatation in dependence on the control voltage amplitude, frequency, temperature, and bias field strength and first experimental results are presented. The effective capacitance, which has been measured with large control amplitudes, determined the output parameters of the control electronic and the stability of the set up. The loss power (loss tangent) influences the heating of the piezo-actuator when large control amplitudes and high frequencies are used. The comprehensive data files from the set-up include many additional information which can be evaluated by a comfortable evaluation software. A loss power hyperbola of pie-actuators is derived being analogous to the loss power hyperbola of transistors. In addition, aging effects were investigated for the effective capacity, the loss power and the dilatation after a complete temperature and electrically field cycle. Harmonic distortion of the actuator current by controlling with large amplitudes and the change of the loss power by controlling with saw tooth and rectangular control voltages have bee measured.
The free and clamped higher order dielectric coefficients of barium titanate (BTi, BSi, CTi, CSi) are determined by measuring the field dependence of polarisation within the double loop region. For this purpose pulses were applied to the samples with rise times which are long and short compared to the transit time of the electrostrictively excited mechanical pulses. The difference BSi–BTi = 4.5 × 108 – (−8) × 108 = 12.5 × 108 m5V/C3 satisfactorily agrees with the value calculated from eletrostrictive and elastic coefficients.
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