Growth, structure and properties of (K1 − x(NH4)x)9H7(SO4)8·H2O crystals

• An influence of isomorphous substitution on anomalies of (K1-x(NH4)x)9H7(SO4)8 · H2O under the phase transitions.

Single crystals of (K1 − х(NH4)x)mHn(SO4)(m + n)/2·yH2O solid solutions are grown in the K3H(SO4)2–(NH4)3H(SO4)2–H2O system which end members are known to undergo superprotonic phase transitions with essentially different kinetics. Replacements in the cation sublattice and their influence on structural transitions as well as dielectric and optical properties of these crystals are of obvious interest both for fundamental and applied physics as new functional materials. Solutions of K3H(SO4)2 and (NH4)3H(SO4)2 with different ratio (K:NH4) crystallize in different structure types. The ratio 1:1 leads to the single crystals, which have the general formula ((K1 − x(NH4)х)9H7(SO4)8·H2O. The grown crystals are characterized and the crystal structure of the (K1 − х(NH4)x)mHn(SO4)(m + n)/2·H2O (x =0.04) crystal is solved. Data comparison for (K1 − х(NH4)x)mHn(SO4)(m + n)/2·H2O and K9H7(SO4)8·H2O crystals allows to establish structural conditionalities of differences in conductivity. One can assume that potassium ions are involved in the conductivity in addition to protons.

An influence of isomorphous substitution on anomalies of (K1 − x(NH4)x)9H7(SO4)8·H2O under the phase transitions as well as dielectric and optical properties of these crystals were studied over the temperature range of 290–420 K. Single crystal structure of (K1 − x(NH4)х)9H7(SO4)8·H2O (x = 0.04) was determined using X-ray diffraction techniques.