An ESR Study of Structural Phase Transitions of(NH₄)₂Pb[Cu(NO₂)₆]

Abstract

The structural changes o f (N H 4) 2P b [C u (N 0 2)6] crystals during the phase transitions at 316, 287, and 95 K were studied by means o f a single crystal ESR technique. Anisotropic g values [9 > 9±) were obtained in the lowest temperature phase IV, whereas the ESR spectra recorded in the intermediate phases III and II, in which the crystal is known to be tetragonally compressed along the c axis, could be interpreted by use o f effective g values [g ( c) < g (_L c)]. In the highest temperature phase I an isotropic g value was obtained. The phases I, II, and III o f the present complex can be assumed to be very similar to the corresponding phases observed above ~ 250 K for the com pounds R2P b [C u (N 0 2) 6] with R = K, Rb, Cs, and Tl. However, the lowest temperature phase transition transforms the phase III with an antiferrodistortive order o f the elongated [C u (N 0 2)6]4_ octahedra into the phase IV with a ferrodistortive one. This occurs only for the complex with R = N H 4 and is very unusual. The results o f the 14N N Q R experiments already reported for the phases III and IV could be well explained by the present newly proposed model.

Chlorine NQR Spin-Lattice Relaxation and Electron Spin Dynamics in Paramagnetic [Co(H2O)6[PtCl6]

“…2, and where is the Bohr magneton, H = (HX, Hy, FF) the external magnetic field, S = (SX, Sy, S.) the electron spin operator, and the others have their usual mean ing [4,5,[26][27][28]. The spectra described by (16) are invariant with respect to the rotation of the field about the [1,1, 1] axis of the crystal, and maximum spread of the spectrum is observed when the magnetic field is parallel to the [1, 1, 1] axis [5], The spin-Hamiltonian parameters determined at room temperature are 9 \\ ~. '-/±= 2.00, |D| = 168 G, M "| = 97G, M J = 96G, and |a| = 8G, in the unit of magnetic field for the electron (1G = 10"4T).…”

“…Mn2+ ESR spectra of a Mn2+ doped single crystal of [Co(H20 )6] [PtCl6] were recorded by use of a JEOL SCXA X-band spectrometer with a TE011 cylindrical cavity resonator [16,17]. From the rotation patterns of the ESR spectra, the [1, 1, 1] axis of the crystal was identified.…”