Twinning in paratellurite crystals

Using optical-polarized method the twinning of paratellurite TeO2 crystals has been observed. This twinning may be explained if to suggest the existence of hypothetical prophase with the cubic symmetry m3m. It is determined that TeO2 crystals may possess three ferroelastic states S-1, S-2, S-3, which differ by the 4-fold axis directions. Every ferroelastic state may contain two ferroelastoelectric states which differ by the components of the spontaneous piezoelectric coefficient tensor (SPCT). If the SPCT's differ by the polarization directions only but do not differ by spontaneous deformations, then such ferroelastoelectric states form dauphine twins. If the SPCT's differ by the polarization directions and spontaneous deformations, then such ferooelastoelectric states form Brazilian twins.