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 microcry stals or ''crystallographic'' strain is measured on lead magnesium nio bate-lead titanate-barium titanate electrostrictive ceramics of compos ition 0.970(0.900PMN-0.100PT)-0.030BT from zero field to saturation. T his crystallographic strain is then compared to the bulk longitudinal strain as measured by Delta l/l using a photonic sensor. The crystallo graphic electric-field induced strain behavior for virgin samples coul d be fit to a constitutive model, where the induced strain is proporti onal to the square of the polarization with an electrostrictive coeffi cient 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 e lectrostrictive coefficient Q similar to 1, and generally yielded wors e fits where the model predicted greater than the observed strain valu es at low electric fields. Subsequent in situ XRD measurements on prev iously electric-field cycled samples yielded much lower crystallograph ic strain values with a significantly different electric field depende nce. (C) 1997 American Institute of Physics.