Further study of the Mn²⁺EPR centre in ferro- and para-elastic BiVO₄:spin Hamiltonian parameters and temperature dependence

Abstract

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+or-0.0009, D/h=2.443+or-0.002, E/h=0.4912+or-0.0009, F/h=0.094+or-0.002, B42/h=0.0, Ax/h=0.27+or-0.02, Ay/h=0.25+or-0.02, and Az/h=0.33+or-0.02 GHz at room temperature (<Tc=528 K); and g=1.994+or-0.001, D/h=0.000+or-0.004, E/h=0.000+or-0.004, F/h=0.00+or-0.01, A/h=0.25+or-0.01 GHz at T=535 K (>Tc). The principal x, y, and z axes of the D-tensor are found to be along the crystallographic b, c+45 degrees and a+45 degrees axes, respectively. This Mn2+ centre has the correct principal axes system of the D-tensor compared with the previous MnI 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.

Low-Symmetry Aspects in EPR Spectra of Mn2+at Bi3+Sites in BiVO4Single Crystal

“…Recently, a number of experiments, e.g. X-ray and neutron diffraction [5], Raman scattering [6][7][8], NMR [9][10][11][12], and EPR [13][14][15][16] have been carried out to investigate structural changes, phase transitions, and optical properties of BiVO4. EPR is a powerful technique in studies of local site symmetry around paramagnetic impurities in crystals.…”

“…EPR is a powerful technique in studies of local site symmetry around paramagnetic impurities in crystals. EPR studies of Gd3+, Er3+, and Mn2+ in BiVO4 single crystals were reported [13][14][15][16]. The site symmetry of Gd 3 + centre in BiVO4 single crystal was determined [13].…”

“…In the present paper, we reanalyse the zerof ield splitting (ZFS) parameters obtained from EPR X-band experiments of Baran's et al [13] and Yeom,s et al [16]. It appears that the two data sets cannot be directly compared.…”

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Zero-field splitting parameters obtained from EPR X-band experiments of and Yeom et al (1992) are reanalyzed. Transformation relations are derived to express the two sets of data in the same axis system.

Problems arising from using a truncated zero-field splitting Hamiltonian in fitting the experimental data are elucidated.

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“…Zero-field splitting parameters obtained from EPR X-band experiments of and Yeom et al (1992) are reanalyzed. Transformation relations are derived to express the two sets of data in the same axis system.…”