³⁵Cl nuclear quadrupole resonance study of anion dynamics in the paraelectric phases of Cs₂ZnCl₄and Rb₂ZnCl₄

Abstract

The dynamics of the ZnCl4 anion in two compounds, one exhibiting a structural transition to an incommensurate phase (Rb2ZnCl4) and another not having any structural transition at all (Cs2ZnCl4), are studied through 35Cl NQR frequency ( nu ) and relaxation time (T1Q) measurements as a function of temperature T in their high-temperature (paraelectric) phases. Estimates of the potential barriers hindering the reorientational motions of ZnCl4 anions along axes parallel and perpendicular to the a axis of the crystal structure are obtained from the T1Q data. These results are analysed in conjunction with a qualitative comparison of relative mean square amplitudes of such motions obtainable from frequency data, in order to investigate the differences in the dynamics and structure of the ZnCl4 anion. There seems to be correlation between the dynamics of the anion in this phase and the possibility that the compound may exhibit a structural instability at low temperatures in this family.

35Cl NQR Study of Phase Soliton Formation and Residual Commensurations in K2ZnCl4

“…This activation, in general, enables one to find out the depth of the confining potential of the anion reorientation, which depends on the complex balance of the interatomic forces and the relative cation sizes hindering the torsional motion around the axis of lattice modulation (the -axis in our case) [8].…”

“…Undergoing the lock-in transition, the incommensurate modulation commensurately locks in to = 0, which leads to a unit cell triplication in the direction of the c-axis [7] with a spontaneous polarization along the a-axis, so that the crystal shows ferroelectricity [5]. It is well known that the important eigencomponents of such a lattice modulation are the rotation of the ZnCl 4 tetrahedra around the c-axis, and the translation of the ZnCl 4 group and the K + ion [8]. Thus, studies of the rotational motion of 0932-0784 / 02 / 0600-0363 $ 06.00 c Verlag der Zeitschrift für Naturforschung, Tübingen www.znaturforsch.com the tetrahedral group are important for understanding the lattice modulation and the incommensurability in A 2 BX 4 systems.…”

“…Recently relaxation studies of NQR and quadrupole-perturbed NMR have been extensively carried out in order to investigate the dynamics of the incommensurate modulation [14 -19, 23] and of the tetrahedral groups [8]. By employing NQR techniques, the shape and depth of the potential confining the tetrahedral anion and hindering its rotational motion can be estimated from the dynamics reflected in the temperature dependence of the spin-lattice relaxation [8].…”

“…By employing NQR techniques, the shape and depth of the potential confining the tetrahedral anion and hindering its rotational motion can be estimated from the dynamics reflected in the temperature dependence of the spin-lattice relaxation [8]. It is the purpose of the present work to throw some light onto the detailed processes and dynamics concerning the formation of the phase solitons and commensurate domains by probing the dynamics of the triplicated ZnCl 4 tetrahedral groups in the lock-in phase by means of 35 Cl NQR spin-lattice relaxation measurements.…”

Structural properties of two inequivalent Cs(1) and Cs(2) sites in perovskite tricaesium pentahalogencobaltate, Cs3CoX5 (X = Cl, Br)

“…[2][3][4][5][6][7][8][9][10][11] In addition, Cs 3 CoX 5 (X=Cl, Br) crystals with the BX 5 type have received significant attention because of the high degree of symmetry in the tetragonal structure of this crystal, which makes Cs 3 CoX 5 the most convenient type of crystal to study the electric and magnetic structures of the [CoX 4 ] 2 cluster. [12][13][14][15][16][17][18][19][20][21][22][23][24] The tetrahedral coordination of nearly all transition metal complex ions (BX 4 ) 2 (B=Co 2+ , Fe 2+ , Cu 2+ ; and X=Cl , Br ) in crystals is approximately distorted from a regular tetrahedral coordination. 15,16 Tetrahedral Co compounds exhibit several characteristics at low temperatures that make them ideal candidates for studying magnetic properties; the situation is very similar for the tetrahedral cobalt salts Cs 3 CoCl 5 and Cs 3 CoBr 5 .…”