Single crystals of dilute manganese-doped α-Zn2SiO4 have been grown hydrothermally and from the melt. ESR spectra have been examined at 9.5 and 35 Gc/sec. Results are interpreted in terms of Mn2+ at two environmentally different sites, having D parameters 729±8 and 413±4 G and E parameters 170±5 and 135±5 G, respectively. The relative population of the two sites appears to be independent of total manganese concentration or method of crystal growth. It is believed that the two sites correspond to substitution of Mn2+ for Zn2+ at two crystallographically nonequivalent zinc positions in the willemite structure.

No abstract

No abstract

No abstract

The negative thermal expansion coefficient (TEC) in FeF2 and the large positive one in VO2, along the c axis, are explained by a model which emphasizes the changes in force constants, resulting from the spatial rearrangement of the electronic charge surrounding the cation, when low-lying electronic states are thermally populated. The TEC data are compared for 14 rutile-type crystals. It is significant that all the compounds studied which involve unequally occupied t2g electronic orbitals display TEC anomalies.