Barium titanate field effects

The contribution to the stress from electromechanical coupling is readily estimated from the constitutive relation [Eq. (4.2)]. Under conditions of uniaxial strain and field, and for an open circuit, we find that the elastic stiffness is increased by the multiplying factor (1 -i- K ) where the square of the electromechanical coupling factor for uniaxial strain, is a measure of the stiffening effect of the electric field. Values of for various materials are for x-cut quartz, 0.0008, for z-cut lithium niobate, 0.055 for y-cut lithium niobate, 0.074 for barium titanate ceramic, 0.5 and for PZT-5H ceramic, 0.75. These examples show that electromechanical coupling effects can be expected to vary from barely detectable to quite substantial. 

The effect of k on d is most clearly demonstrated in the experiment by Fukada and Date (1970) on the polyester resin film, filled with powdered barium titanate and polarized under a d.c. field. The strong piezoelectricity, as shown in Fig. 29, is ascribed to the polarization charge of the ceramic filler and heterogeneous strain due to the composite structure. The real part d exhibits a maximum at 90° C and d" has a peak and a succeeding dip at this temperature where the primary relaxation of polyester resin occurs. The behavior of d and d" is quite similar to that of k and k" in Fig. 16, respectively, in which decreasing X = an corresponds to increasing temperature. 

Another circumstance is when deterioration becomes apparent under fields in excess of 0.5 MVm-1 at temperatures above 85 °C, and occurs more rapidly the higher the field or the temperature. The fall in resistance has been observed in single crystals of rutile and barium titanate and so must be assumed to be a bulk rather than a grain boundary effect, although there is evidence that grain boundaries play a part in degradation processes in ceramics. 

There are many different kinds of acoustical probes including microphones [57-62], hydrophones, radiometers, and piezoelectric devices (most often small barium titanate transducers) [63-68], and the hot wire microphone (based on acousto-resistive effect) [63], Their resonance frequency is generally very different from that of the ultrasonic field under study. 

EFFECT OF A CONSTANT ELECTRIC FIELD ON THE THERMAL CONDUCTIVITY OF CERAMIC SAMPLES OF SOLID SOLUTIONS BASED ON BARIUM TITANATE AND OF A TRIGLYCINE SULFATE SINGLE CRYSTAL IN THE REGION OF PHASE TRANSITIONS. 

J.Y. Fu, Z. Zhu and L.E. Cross, Experimental studies of the converse flexoelectric effect induced by inhomogeneous electric field in a barium strontium titanate composition, J. Appl. Phys. 100(2), 024112/1-6, (2006). 

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