Phase transitions and the Jahn-Teller effect in Tl₂PbCu(NO₂)₆

The structure of two crystals of rubidium lead hexanitrocuprate(II)

“…Preliminary structural data on KzPbCu(NO2)6 indicate a compressed tetragonal CuN6 configuration below 281K (Takagi et al, 1974), in agreement with single-crystal e.p.r, spectra and X-ray powder data . A compressed tetragonal configuration (14) 1"73 (13) 1"31 (11) has also been found in TIEPbCu(NO2) 6 below 291K (Harrowfield, Dempster, Freeman & Pilbrow, 1973). These structural results suggest that a compressed tetragonal environment for CuN 6 can occur when M' is Pb.…”

Gel Growth of K2PbCu(NO2)6-Elpasolite Single Crystals

“…K 2 PbCu(NO 2 ) 6 belongs to the crystal system of the elpasolite family, with composition A 2 BM(NO 2 ) 6 , where A = K, Rb, Cs, Tl; B = Ca, Sr, Ba, Pb; and M = Fe, Co, Ni, Cu. These systems have been studied extensively, and especially the copper elpasolite K 2 PbCu(NO 2 ) 6 has attracted special interest as it exhibits successive phase transitions due to the cooperative Jahn−Teller effect.…”

“…In particular, K 2 PbCu(NO 2 ) 6 undergoes two successive structural transitions at 281 and 273 K which were previously investigated using electron paramagnetic resonance (EPR) techniques. 6 On the basis of precise X-ray and neutron measurements, Noda et al found that the K 2 PbCu(NO 2 ) 6 elpasolite phase transitions proceed from the face centered cubic phase 1 to the tetragonal phase 2 at 281 K with the c-axis shortened, and to phase 3 with a symmetry lower than orthorhombic, due to the cooperative Jahn−Teller effect. 1 It was further noticed that K 2 PbCu(NO 2 ) 6 is also a potential candidate hosting one-dimensional (1D) antiferromagnetic chains with S = 1/2 per Cu 2+ due to the Cu orbital order induced by the Jahn−Teller distortions.…”

Investigations of EPR g Factors and Rhombic Distortion for the Rhombic Cu2+ Centers in K2Zn1−x Cu x F4 Crystals at Low Temperature

“…centers in K 2 ZnF 4 (i.e., K 2 Zn 1-x octahedra in other crystals, the g // is significantly greater than the value predicted by the theory based on the ground state jd z 2[ , so these g factors for the tetragonally compressed Cu 2? octahedra in crystals are explained in terms of the vibronic coupling between the ground state jd z 2[ and an appropriate excited state jd x 2 Ày 2[ [3,[6][7][8]. The rhombic distortions of Cu 2?…”