EPR AND ENDOR INVESTIGATION OF SINGLE-CRYSTALLINE AND POWDERED NACL-RH2-RH2+( AND AGCL)

Single crystalline NaCl doped with Rh2+ was investigated with electron paramagnetic resonance (EPR) and electron nuclear double resonance (E NDOR). An orthorhombic Rh2+ centre was found similar to that observed previously in AgCl, where Rh2+ substitutes for Na+ forming an [RhCl6]( 4-) complex elongated along a [001] axis with a charge compensating Na + vacancy in a second nearest Na+ position in the equatorial plane. In addition, two further axial Rh2+ centres were found, where the Na+ va cancy is not in the nearby equatorial plane. In the powder ENDOR spect ra of NaCl:Rh2+ the interactions with axial second nearest Na-23 and a xial Rh-103 nuclei could be resolved. Powder ENDOR spectra of AgCl:Rh2 + precipitated from aqueous solution showed that the Rh2+ defect is di fferent from that generated in Rh2+-doped AgCl grown from the melt. Th e limitations and possibilities of powder ENDOR are discussed. (C) 199 7 Elsevier Science Ltd.