Effect of hydrostatic pressure and temperature on the EPR spectrum of the Mn2+ ion in Zn(BF4)2 · 6H2O

A study of the effect of hydrostatic pressure and temperature on the EPR spectrum of the Mn2+ ion in Zn(BF4)2 · 6H2O is reported. The break in the temperature dependence of the b20 parameter at 196 K is evidence of the existence of a phase transition accompanied by a change in the thermal expansion coefficient. It is shown that pressure considerably affects the spectral parameters by reducing the axial parameter b20 and increasing the cubic one, b40. At 9 kbar, the b20 parameter is temperature independent. A comparison of the pressure dependences of the spectra of Zn(BF4)2 · 6H2O, ZnSiF6 · 6H2O, ZnTiF6 · 6H2O, and MgSiF2 · 6H2O 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 formation of satellites at each EPR line, their separation being proportional to the magnetic field. The nonlinear pressure dependence of the linewidth is related to the structural features of the crystal under study.