Richard H. Langley

Lattice parameters and ionic radii of the oxide and fluoride garnets

Abstract An equation relating ionic radii and lattice parameters for compounds with the garnet structure has been fit to over 330 representative formulations. The radii of the anions, together with the radii and lattice sites of cations, are taken into account. This mathematical relationship can be used to test data, to assist in the assignment of cations to symmetry sites, to predict lattice parameters of unknown compositions, and to suggest the feasibility of preparing compounds with specific compositions. Previously unreported cationic radii for eight-coordinate Cu(I) and four-coordinate Co(III) and Fe(IV) as well as the radii of vacancies in the garnet structure are discussed.

Structure and phase transitions of the lanthanide metals

The structures and phase transitions of the lanthanide metals can be related to f orbital contributions to the bonding. With increasing availability of the f orbitals the structure sequence hexagonal closest packed, double hexagonal closest packed, δ-samarium, cubic closest packed, and body-centered cubic is observed. Increases in temperature and/or pressure result in an increased availability of the f orbitals resulting in predictable phase transitions.

Synthesis of transition-metal fluoride garnets

Abstract The preparation of the fluoride garnets of the first-row transition metals (Na3M2Li3F12) has been studied. The fluoride garnets of manganese (III) and nickel (III) are reported for the first time, leaving only copper (III) garnet unachieved. By using a guideline based on the electronic configuration of the transition metal ion and its site symmetry in the cubic structure, the ease or difficulty of preparation of these garnets is systematized.

Infrared spectra of fluoride garnets

Abstract The i.r. spectra of a series of first-row transition metal fluoride garnets (Na 3 M 2 Li 3F 12 ) have been studied in the region 4000 –50 cm −1 . The vibrational frequencies are grouped into two classes: those which depend upon the unit cell edge, or the size of the transition metal ion; and those showing no such dependence. The bands which depend upon the transition metal ion are assigned to the normal modes of an octahedral group which have been split by the crystallographic site symmetry, S 6 . Of the seventeen modes predicted by factor group analysis, fourteen were observed. The assignments of these frequencies differ in some cases from those previously reported. Several data involving the inactive ν 6 mode of the nominal octahedron are reported.