Spontaneous strain in ferroelectric triglycine sulphate crystals: EPR studies of vanadyl impurities. Part II

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Abstract
In ferroelectric TGS crystals, EPR spectra of polar VO2+ impurities exhibit doublet splittings with unequal intensities on each of the 51V hyperfine lines. While the intensity ratio depends on vanadyl dipole relaxation in the spontaneous local field E(T), the corresponding strain in TGS lattices is considered to be responsible for the displacement of VO2+ axes. The strain tensor e determined from the VO2+ spectra is expressed as e = dE(T), where the tensor d consists of local strain coefficients at the impurity site. Unlike macroscopic piezoelectric strain coefficients defined for an externally applied field, these d-tensor elements indicated no temperature dependence. The function E(T) studied from VO2+ displacements and 51V hyperfine splittings is found to be proportional to the spontaneous polarization PS(T), being consistent with the previous result obtained from the doublet intensity ratio.

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