An EPR study of an S = 3/2 defect in CaWO₄

Abstract

After n-irradiation of CaWO, up to a dose of 3 x 1OlB nvt a spectrum consisting of 12 narrow lines is observed. The angular variation of the spectrum shows that a centre with S = 312 located at four magnetically inequivalent sites in the structure is involved. The data are consistent with a spin Hamiltonian X = B S . g . B + S . D . S , where g and D are noncoincident with principal values gz = 2.048, gv = 2.007, gz = 2.004, D, = 4.32 x cm-', D, = 0.31 x low4 cm-l and D, = -4.63 x lo-' cm-l. Possible intrinsic lattice defects which might account for this spectrum are discussed. Nach Neutronenbestrahlung bis zu einer Dosis von 3 x nvt wurde in CaWO, ein Spektrum aus 12 schmalen Linien beobachtet. Die WinkelabhLngigkeit des Spektrums zeigt, da13 ein Zentrum mit S = 312 an vier magnetisch aquivalenten Platzen der Struktur beteiligt ist. Die Werte sind mit einem Spin-Hamiltonian 3 t ' = j3 S . g -B + S D . S konsistent, wobei g und D nicht koinzidieren mit den Hauptwerten gz = 2,048; g, = 2,007; gz = 2,004; D, = 4,32 x cm-l und D, = -4,63 x lo-, crn-l. Mogliche gittereigene Defekte, die fur dieses Spektrum verantwortlich sind, werden diskutiert. cm-'; D, = 0,31 x

Low-symmetry effects in electron paramagnetic resonance

“…g, however, depends on the electron distribution of the whole molecule and so they concluded that there was no special reason to require g and A axes to be coincident. Weightman et al (1972) reported an S = 8 defect centre in irradiated Caw04 for which g and D were found to have different principal axes. They were unable completely to characterise the centre but supposed that g and D orientations were due to different mechanisms but without being very specific about what they might be.…”