Phase transitions in the (Cs1-xRbx)(2)Znl(4) system

(Cs1-xRbx) 2ZnI4 crystals were grown by two different methods with Rb conce ntrations varying from x=0 to 2.5%. I-127 NQR and calorimetric measurements showed that crystals grown by the Bridgman technique contain residual impu rities (similar to 0.5%) for all x. While x=0 crystals grown from solution do not contain detectable impurities, they allow incorporation only of a lo w Rb concentration, not above 0.5%. A transition-temperature-concentration (x) phase diagram has been constructed for Bridgman-grown crystals from NQR data. Rb doping shifts the normal-incommensurate and incommensurate-ferroe lastic phase-transition points toward higher temperatures with different ra tes. The P2(1)/m<->P1 first-order transition shifts toward lower temperatur es. The region of low Rb concentrations lies closest to the critical point. (C) 1999 American Institute of Physics. [S1063-7834(99)03001-4].