Effect of hydrostatic pressure and temperature on the EPR spectrum of the Mn2+ ion in Zn(BF4)(2) center dot 6H(2)O

A study of the effect of hydrostatic pressure and temperature on the EPR sp ectrum of the Mn2+ ion in Zn(BF4)(2) . 6H(2)O is reported. The break in the temperature dependence of the b(2)(0) parameter at 196 K is evidence of th e existence of a phase transition accompanied by a change in the thermal ex pansion coefficient. It is shown that pressure considerably affects the spe ctral parameters by reducing the axial parameter b(2)(0) and increasing the cubic one, b(4)(0). At 9 kbar, the b(2)(0) parameter is temperature indepe ndent. A comparison of the pressure dependences of the spectra of Zn(BF4)(2 ) . 6H(2)O, ZnSiF6 . 6H(2)O, ZnTiF6 . 6H(2)O, and MgSiF2 . 6H(2)O crystals suggests equal hydrogen-bond lengths in these compounds. A ligand hyperfine structure has been detected, which originates from the Zeeman interaction with the proton nuclei surrounding Mn2+ and manifests itself in the formati on of satellites at each EPR line, their separation being proportional to t he magnetic field. The nonlinear pressure dependence of the linewidth is re lated to the structural features of the crystal under study. (C) 2000 MAIK "Nauka/Interperiodica".