Hydrogen-bonded ferroelectrics: evidence for Slater configurations from E.P.R. studies of X-irradiated KH<SUB>2</SUB>AsO<SUB>4</SUB> and NH<SUB>4</SUB>H<SUB>2</SUB>AsO<SUB>4</SUB>

The temperature dependence of the powder E.P.R. spectrum of the AsO<SUB>4</SUB><SUP>4-</SUP> centre in x-irradiated samples of KH<SUB>2</SUB>AsO<SUB>4</SUB> and NH<SUB>4</SUB>H<SUB>2</SUB>AsO<SUB>4</SUB> yields results which can be understood as arising from exchange processes taking place between the six configurations in the Slater model for this type of hydrogen-bonded ferroelectric and antiferroelectric. Knowing that the <SUP>75</SUP>As hyperfine parameters have rhombic symmetry in the compounds studied, it is possible to interpret certain specific features in the spectra as being associated with the Slater configurations of higher energy