Electrical conductivity of acid crystallohydrate MgHPO<inf>4</inf>· 3H<inf>2</inf>O and its structural transformations

Abstract

Electrical and thermal characteristics of solid MgHPO4· 3H2O have been investigated in a temperature interval from 20-400°C, and correlated with data of X-ray diffraction analysis. It is noted that in the temperature interval from 20-140°C, despite the presence of considerable hydrogen concentrations, the sample shows very small electrical conductivity. This is a consequence of crystal structure, where the strongest hydrogen bond exists between acid proton and oxygen of P043- group. So a strong hydrogen bond decreases the number of potential electric carriers and prevents rotation of the P043-acceptor group, which causes crystallohydrate to show poor conductivity. With the breakage of crystal structure, caused by dehydration, amorphous MgHPO4, salt is formed and conductivity abruptly increases. At about 550°C crystallization starts and the newly formed phase Mg2P2O7 again shows poorer conductivity. © 1988.