V. E. Petrashen

EPR of the first Fe(III)-containing spin-crossover metallomesogens

The low-spin (LS) to high-spin (HS) transition in two mesogenic Fe(III) complexes with alkyloxysalicyliden-N′-ethyl-N-ethylendiamine as ligands is studied by electron paramagnetic resonance (EPR). The symmetrization of the crystal field around the Fe(III) ion under first heating of a polycrystalline sample from the room temperature was observed in the spectra of HS complexes. The line narrowing (from 45 to 15 mT) under the crystal-smectic phase transition is explained by the strengthening of the intermolecular exchange interaction, as a result of the structural reorganization of layers in the smectic phase. A feature of both mesogenic spin-transition systemsis an unusual field-induced spin instability which leads to the hysteresis of the HS-LS composition. This instability is detected by EPR and magnetic susceptibility methods. The alignment of systems by magnetic field in the mesophase and a complete or partial orientational order under cooling the mesophase to the glass state are the main reason for this hysteresis. The influence of EPR-silent LS complexes reveals itself in the line broadening of HS compounds’ when the temperature is lowered from 220 K.

Continuous changes of the Jahn-Teller deformation of Cu(H2O)6 complex in ferroelastic Cs2Cu(ZrF6)2.6H2O crystal

Abstract Q-band EPR spectra of Cs 2 Cu(ZrF 6 ) 2 ·6H 2 O measured in temperature range 4.2–350 K and supported by the X-ray crystal structure analysis, show a gradual transformation of an adiabatic potential surface of the Jahn–Teller (JT) Cu(H 2 O) 6 2+ complex leading to the switch of its elongation direction. This effect is joined with a ferroelastic phase transition at 320 K. It is shown that gradual movement of minima of the adiabatic potential surface along the φ coordinate for ρ ≅ ρ 0 , describing this phenomenon, is a result of a competition between a small lattice deformation at T > T c and the new deformation appearing at T c and increasing with decreasing temperature.

Jahn-Teller effect in low-spin Ni3+ in the LaAlO3 ceramic

This paper reports on an EPR study of LaAl1−xNixO3 solid solutions with x≤0.12 made in the 4.2-to 300-K temperature range. In the X range, the broadening of the single EPR line with geff=2.148 was observed at temperatures below ∼40 K. In the Q range, a slightly anisotropic EPR line with g⊥′=2.145±0.002 and g‖′=2.154±0.002 transforms to a rhombic-symmetry spectrum with g1=2.183±0.002, g2=2.143±0.002, and g3=2.118±0.002. It is shown that the observed low-temperature effects are due to the lowered symmetry of the complex under the combined action of the tetragonal Jahn-Teller distortions and of the trigonal component of the crystal field.

EPR and X-Ray Studies of the Vibronic Effects in Cs2Cu(ZrF6)2.6(H2O) Crystal

EPR and x-Ray studies of Cs2Cu(ZrF6)26(H2O) are reported with special attention paid to the structural phase transitions as a function of temperature and pressure.

X-ray diffractometry and electrical conductivity of the ceramics LaSrAl(Cu,Ni)O4

A continuous series of solid solutions LaSrAL1−xMexO4 (Me = Cu, Ni) has been investigated by x-ray diffractometry and by electrical conductivity measurements. The results are of interest from the standpoint of the theory of close-packing, percolation theory, and the theory of the cooperative Jahn-Teller effect.

The Influence of the Parameters of Lattice Structure on the Configuration of Jahn-Teller Centers

EPR of Cu(H2O) 6 2+ Jahn-Teller (JT) centres in dia- and paramagnetic crystals of Tutton salts M2(I)Zn1−x Cux(ZrF6)2·6H2O(A) and M2(I)Zn1−xCux(SO4)2·6H2O(B) with M=K, Rb, Cs, NH4 (x=0.01, 0.1, 1) was studied over the temperature range 300+4.2 K at X- and Q-bands. A dynamic JT nature of Cu(H2O) 6 2+ centres was established in all Tutton salts.