EPR Study of V4+Ions in Tungsten Trioxide WO3

The EPR spectra from V 4+ ions in WO 3 single crystal were studied in the temperature range from 300 K to 77 K by using a K-band spectrometer. At 77 K, the g values and hf parameters A of V 4+ ions were strong c -axis anistropy, so that g X =1.928, g Y =1.945, g Z =1.815, (Eulerian angles; θ g =3.9°, φ g =45.8°, ψ g =-0.2°), and A X =-60.5 G, A Y =-55.0 G, A Z =-190.4 G, (θ A =4.4°, φ A =43.6°, ψ A =1.5°). The ground state of 3 d 1 electron of V 4+ ion was determined to be | x y > state by hf structure analysis. WO 3 is determined to be a ferroelectric material with the spontaneous polarization along the c -axis connected to the condensed ferroelectric \(₁₅ᶻ\) phonon modes of W 6+ ions in the monoclinic II phase at 77 K. At the relations of g av vs A iso for V 4+ and VO 2+ ions in some host crystals, WO 3 is shown to be a remarkable material.