Proton conductivity and spontaneous strain below superprotonic phase transition in CsH2PO4

Electrical conductivity and X-ray measurements have been carried out in order to reveal the origin of the relatively high electrical conductivity observed in CsH2PO4 below the superprotonic phase transition temperature Tc (= 513 K). The electrical conductivity increases at around 400 K with increasing temperature. Moreover, component d of the spontaneous strain tensor obtained from the X-ray diffraction data steeply decreases at around 400 K. From these results, it is deduced that the appearance of proton conductivity even below Tc is closely related to the decrease in the spontaneous strain.