In situ investigation of the non-linear optical crystal rubidium titanyl arsenate, RbTiOAsO₄, under applied electric field using X-ray imaging

Recent work on the non-linear optical single-crystal rubidium titanyl arsenate (RbTiOAsO₄, RTA) has shown that it exhibits behaviour consistent with a ferroelectric semiconductor under large applied electric fields, with the development of a non-uniform field in the near-surface region. To confirm aspects of the proposed model, the behaviour of 001 slices of initially single-domain RTA, patterned with periodic Ag electrodes of spacing 38 µm, as for periodic poling in non-linear optics, were investigated using synchrotron X-ray section topography with the electric field applied in situ while under X-ray illumination at the ID19 topography beamline of the ESRF, Grenoble. The results of white-beam section topography as both a function of crystal to film distance, and under DC voltage are reported, confirming that there is a bending of the planes in the near-surface region. The strain in the near-surface region was examined directly using high-resolution monochromatic X-ray section topography. This revealed an extensive strain of 3 (±1) × 10⁻⁴ at 1 kV, indicating that the electrostrictive coefficient, γ₃₃₃₃, in RTA is positive in sign.