EPR STUDIES OF CR3+ AND FE3+ IN HOST CRYSTALS WITH LANGBEINITE STRUCTURE

Electron paramagnetic resonance (EPR) spectra of trivalent chromium an d iron ions have been investigated in host crystals of double sulfates with langbeinite structure, A(2)B(2)(SO4)(3), with A = NH4+, Rb+, Tl and B = Cd2+, Mg2+. In most cases, single crystals could be grown, an d the spin Hamiltonian parameters have been determined from the rotati onal diagrams. Powder spectra were analyzed and simulated as well. Thr ee centres of axial symmetry with different zero field splittings have been observed for Cr3+, and two for Fe3+. The trivalent impurity ions have been shown to occupy divalent lattice sites substitutionally, bu t the environments are different depending on the structure and the me chanism of charge compensation. A qualitative description of the incor poration of dopants has been possible on this basis, taking into accou nt the local relaxation and the ligand field stabilization effects. Te mperature dependent single crystal and powder measurements have provid ed information on the zero field splitting and phase transitions.