Role of NH(4) ions in successive phase transitions of perovskite type (NH(4))(2)ZnX(4) (X = Cl, Br) by (1)H MAS NMR and (14)N NMR

The (1)H chemical shifts and the spin-lattice relaxation time, T(1ρ), in the rotating frame of (NH(4))(2)ZnX(4) (X = Cl, Br) are observed in order to investigate local phenomena related to successive phase transitions. The temperature dependence of T(1ρ) values for (1)H showed a minimum, and the T(1ρ) values for (1)H appeared to be governed by tumbling molecular motions at high temperatures. In addition, (14)N NMR spectra are studied in each phase of (NH(4))(2)ZnX(4) single crystals in the laboratory frame. The phase transition temperatures strongly affect the (14)N number of symmetry related nitrogen centers within the unit cell. The (1)H MAS NMR and (14)N NMR results are discussed to elucidate the roles of NH(4) ions during the phase transitions of (NH(4))(2)ZnX(4).