Strain gradient induced polarization in SrTiO3 single crystals

Piezoelectricity is inherent only in noncentrosymmetric materials, but a piezoelectric response can also be obtained in centrosymmetric crystals if subjected to inhomogeneous deformation. This phenomenon, known as flexoelectricity, affects the functional properties of insulators, particularly thin films of high permittivity materials. We have measured strain-gradient-induced polarization in single crystals of paraelectric SrTiO$_3$ as a function of temperature and orientation down to and below the 105 K phase transition. Estimates were obtained for all the components of the flexoelectric tensor, and calculations based on these indicate that local polarization around defects in SrTiO$_3$ may exceed the largest ferroelectric polarizations. A sign reversal of the flexoelectric response detected below the phase transition suggests that the ferroelastic domain walls of SrTiO$_3$ may be polar.Comment: 4 pages, 3 figures, 1 tabl

A combined X-ray scattering and simulation study of halothane in membranes at raised pressures

a b s t r a c t Using a combination of high pressure wide angle X-ray scattering experiments and molecular dynamics simulations, we probe the effect of the archetypal general anaesthetic halothane on the lipid hydrocarbon chain packing and ordering in model bilayers and the variation in these parameters with pressure. Incorporation of halothane into the membrane causes an expansion of the lipid hydrocarbon chain packing at all pressures. The effect of halothane incorporation on the hydrocarbon chain order parameter is significantly reduced at elevated pressure