Isotropic shrinkage of the oxygen octahedron in SrTiO₃ under uniaxial pressure

X-ray absorption spectra at the Ti K-edge of a SrTiO₃ single crystal under uniaxial pressure were measured to obtain evidence of uniaxial pressure-induced polarization predicted in SrTiO₃ from the electronic viewpoint. The pre-edge 3d-e _g peak decreases in intensity with increasing uniaxial pressure, together with an energy shift to higher energy side. Contrary to uniaxial deformation, these changes were independent of incident x-ray polarization. This implies the presence of a mechanism that maintains the isotropic coordination environment around a Ti atom, i.e. a tilt and rotation of the TiO₆ octahedron accompanied by its isotropic shrinkage, hence the local polarization essential to the ferroelectric order cannot be observed.