Surface transformation of ferroelectric LiH3(SeO3)2 and topochemical nature

The high-temperature phenomenon of ferroelectric LiH3(SeO3)(2) was studied by thermal analyses and impedance spectroscopy. Differential scanning calorimetry reveals an anomalous increase at about 70 degreesC in agreement with thermogravimetry and a peak at 114 degreesC. Dielectric constant and electrical conductivity show an anomaly at about 87 degreesC and 105 degreesC. The large and irreversible thermal hysteresis in dielectric constant and electrical conductivity is interpreted in terms of proton transport and thermal decomposition. Optical observation showed a drastic surface transformation. Present study indicates that the high temperature anomaly around T-d is controlled by topochemical factors.