Investigation of crystallographic and bulk strain in doped lead magnesium niobate

Using an in situ x-ray diffraction (XRD) technique, the electric-field induced change in the d-spacings Delta d/d of the individual microcrystals or ''crystallographic'' strain is measured on lead magnesium niobate-lead titanate-barium titanate electrostrictive ceramics of composition 0.970(0.900PMN-0.100PT)-0.030BT from zero field to saturation. This crystallographic strain is then compared to the bulk longitudinal strain as measured by Delta l/l using a photonic sensor. The crystallographic electric-field induced strain behavior for virgin samples could be fit to a constitutive model, where the induced strain is proportional to the square of the polarization with an electrostrictive coefficient Q determined to be 1.4 (x 10(6) cm(4)/C-2). Attempts to fit the bulk strain behavior on the same sample required lower values of the electrostrictive coefficient Q similar to 1, and generally yielded worse fits where the model predicted greater than the observed strain values at low electric fields. Subsequent in situ XRD measurements on previously electric-field cycled samples yielded much lower crystallographic strain values with a significantly different electric field dependence. (C) 1997 American Institute of Physics.