Etude spectroscopique des ions cuivre (II) en coordinence tétraédrique dans les silicates synthétiques de type milarite

ESR spectra of copper-containing silicates Na ₂Mg _{5- x}Cu _xSi ₁₂O ₃₀ with a milarite structure have been recorded at two frequencies (X band and Q band) and at several temperatures in the range 298-77K. For x less than 0.5 the well-resolved powder spectrum is characteristic of tetrahedral copper ions in orthorhombic symmetry with g_zz = 2.517; g_xx = 2.135; g_yy = 2.091. The hyperfine structure is completely resolved at 77K ( A_zz = 45.9 × 10 ^-4cm ^-1; A_yy = 23.0 × 10 ^-4cm ^-1; A_xx = 41.0 × 10 ^-4cm ^-1). The ESR parameters may be interpreted in terms of an admixture of 4 p_z wavefunction into the 3 d_xy ground state. The results are in good agreement with diffuse reflectance spectra and crystal field calculations.