FURTHER STUDY OF THE MN2+ EPR CENTER IN FERRO-ELASTIC AND PARA-ELASTIC BIVO4 - SPIN HAMILTONIAN PARAMETERS AND TEMPERATURE-DEPENDENCE

The electron paramagnetic resonance (EPR) of an Mn2+ (S = 5/2) impurity in the ferroelastic and para-elastic phase of BiVO4 crystals with a single domain, grown by the Czochralski method, has been investigated using an X-band spectrometer. The rotation patterns of the resonance fields measured on the crystallographic planes are analysed: g = 1.9940 +/- 0.0009, D/h = 2.443 +/- 0.002, E/h = 0.4912 +/- 0.0009, F/h = 0.094 +/- 0.002, B(4)2/h = 0.0, A(x)/h = 0.27 +/- 0.02, Ay/h = 0.25 +/- 0.02, and A(z)/h = 0.33 +/- 0.02 GHz at room temperature (< T(c) = 528 K); and g = 1.994 +/- 0.001, D/h = 0.000 +/- 0.004, E/h = 0.000 +/- 0.004, F/h = 0.00 +/- 0.01, A/h = 0.25 +/- 0.01 GHz at T = 535 K (> T(c)). The principal x, y, and z axes of the D-tensor are found to be along the crystallographic bBAR, c + 45-degrees and aBAR + 45-degrees axes, respectively. This Mn2+ centre has the correct principal axes system of the D-tensor compared with the previous Mn(I) centre. The D-value decreases as the temperature increases in the range 107-535 K. It is proposed that the Mn2+ ion substitutes for Bi3+ without nearby charge compensation.