The existence of ferroelectric-antiferroelectric fluctuations in Rb_1-x(NH₄)_xH₂PO₄

By taking ⁷⁵As hyperfine coupling constants for AsO₄^4- in hydrogen bonded crystals of RbH₂PO₄ and (NH₄)H₂PO₄ as fingerprints of ferroelectric (FE) and antiferroelectric (AFE) phases respectively, it is shown that the variation of the coupling constant as a weighted average of Rb⁺ and NH⁴+ concentrations in Rb_1-x(NH₄)_xH₂PO₄ clearly proves the existence of FE and AFE fluctuations in the mixed crystal.