Investigation of an x -ray diffraction-based technique for measurement of electrostrictive strains

Electrostriction is a materials property which relates the strain response of a crystal to an applied electric field. The strain is independent of the directional sense of the applied field, and is proportional to the square of the field strength. The atomic-level origin of electrostriction is not well understood. A greater understanding of the phenomenon would be assisted by the existence of a direct, non-destructive, non-electrical, high-resolution technique to measure electrostrictive strain. In this work, a technique for measuring electrostrictive strains in crystals using x-ray diffraction (XRD) is investigated. Measurements were made on single crystal and polycrystalline alpha-quartz samples of 115 to 500 μm thickness (SiO2) and single crystal strontium titanate (SrTiO3, or STO) of 500 μm thickness, with metallic silver (Ag) blocking electrodes. Strain-field behavior in alpha-quartz indicated an electrostrictive coefficient M33 = +4 × 10 −18 m2V−2 for 500-μm crystals. However, strain-field behavior was not detectable in single-crystal quartz samples of less than 500 μm thickness. Strain-field response measured in STO was independent of the direction of the applied electric field, which is consistent with electrostriction. However, the strain-field response did not show the quadratic relation expected for electrostriction. The discrepancy between the observed and expected results in STO is attributed to ionic drift in the sample, coupled with local-field amplification effects caused by the interaction of blocking electrodes with ionic dielectric materials. The suggested reason for this discrepancy is that local field within the crystal is increased due to an increase in the resistivity of the ionic dielectric material near the electrode. To test the ionic drift hypothesis offered in this work, experiments using time-resolved XRD and alternating-polarity applied field are suggested