D0103

FERROELECTRIC SWITCHING, ATOMIC DISPLACEMENTS AND PIEZOELECTRIC MODULI IN CTA (CsTiOAsO₄) AND KTP (KtiOPO4). Jörgen Albertsson,^a Kenny Ståhl,^b Jonathan C. Hanson,^c Göran Svensson^a, Rindert Bolt.^{a a}Inorganic Chemistry, CTH, S-412 96 Göteborg, Sweden; ^bChemistry Dept. B, DTU, DK-2800 Lyngby, Denmark; ^cChemistry, BNL, Upton, NY 11973, USA

Peak shifts in selected reflections of extended face crystals of CTA and KTP under a square-wave electric field, have been measured aiming at a determination of (i) the field strengths necessary to switch the ferroelectric domain and (ii) the values of the piezoelectric coefficients. The difference in intensity between the two parts of a split peak of CTA was measured by repeated w scans for 20 c values, 0.05deg. apart. While the peak shifts are caused by the variation in elastic strain with the electric field, differences in intensity correspond to the atomic displacements induced by the field.

Single crystals of CTA and KTP were grown from self fluxes by the top seeded solution growth technique. They were cut and polished to {001} plates with a thickness between 300 and 450 mu. Layers of ca. 200 Å of Au or Al was evaporated onto the {001} faces. The crystals were mounted on the diffractometer at beam line X7B at the National Synchrotron Light Source at Brookhaven National Laboratory (USA), with electric leads connecting the metal layers to a power supply and a generator producing a square-wave variable voltage up to 1500 V. The tension was alternatingly applied to each side of the crystal at a frequency of 20 Hz. A scaler and a clock were gated to each of the two square-waves thus allowing the detection of a possible shift in position and intensity of a reflection between the two field directions. Experiments at low temperature were made with the crystal mounted on the cold finger of a Displex^reg. closed-cycle refrigerator within an evacuated Be can.

Both CTA and KTP crystallizes in space group Pna2₁ with Z = 8. The unit cell dimensions are a = 13.486(2), b = 6.8616(7), c = 10.688(1) Å (CTA) and a = 12.819(3), b = 6.399(1), c = 10.584(2) Å (KTP).