Electrical conductivity of insulating SrTiO3 and LaGaO3 at phase transitions

We have studied the extremely small conductivity of the nominally stoichiometric insulating single crystals LaGaO3 and SrTiO3 in the dark. The conductivity of the LaGaO3 and SrTiO3 crystals exhibits activation type temperature dependence. We have found that the conductivity of the LaGaO3 crystal changes at the ferro-elastic-like phase transition. However, unlike the our previous report on the insulating BaTiO3 and relaxor ferroelectric single crystals, the conductivity of both LaGaO3 and SrTiO3 crystals do not peak. Therefore, the ferroelectric phase transition or the existence of the spontaneous polarization is essential for the peaking in the conductivity-temperature characteristics to occur.