I. Mayer

High-temperature X-ray study of rare-earth silicides

Abstract The structures of AlB 2 and Mn 5 Si 3 -type hexagonal and Cr 5 B 3 and ThCr 2 Si 2 type tetragonal rare-earth silicides have been investigated by a high-temperature X-ray diffraction method in the temperature range 20 °–1200 °C. Thermal expansion coefficients and transition products of the different compounds are given.

The crystal structure of the MAu2Si2 rare earth compounds

Abstract MAu2Si2 type compounds of the LaEr rare-earth metals crystallize in the ThCr2Si2-type body-centered tetragonal structure. Lattice constants and atomic parameters were determined, and the interatomic distances calculated and compared with corresponding data of MAg2Si2 compounds. The radii R AU = 1.36 A and R ag = 1.18 A found are very close to the ionic radii of these atoms. The radii of silicon has the value of the atomic radius in the silver compounds and the covalent radius in the gold compounds.

Rare earth-iron(cobalt, nickel)-silicon compounds

Abstract MSi1.6(Fe, Co, Ni)0.4 compounds (M = La-Gd) have been found to crystallize in the AlB2-type hexagonal structure. X-ray intensity data prove that the transition metal atoms replace part of the silicon atoms of the stoichiometric MSi2. The Mossbauer spectrum of LaSi1.6Fe0.4 shows the iron as closely divalent, with equal distribution of iron atoms between two symmetrically different sites.

Europium silicides and germanides of the EuM2X2 type

Abstract X-ray diffraction studies of EuM2X2 compounds (M = Fe, Co, Ni, Cu; X = Si, Ge) revealed that these compounds crystallize in the ThCr2Si2 type body-centered tetragonal structure, with the space group I4 mmm . Distribution of the atoms among the lattice sites, the free parameter of the Si and Ge atoms, and the interatomic distances of the compounds were determined by crystal structure calculations. Europium, as determined by Mossbauer spectroscopy, is present in the di- and tri-valent states in the EuM2Si2 compounds, the relative amounts of the two states being different in each of the compounds. In EuNiSi3, EuNi2Ge2 and EuCu2Ge2 all the Eu are divalent. The relationship between the structure properties and the valence states of Eu in the compounds is discussed.

MPt2Si2 compounds of the ThCr2Si2 type

Abstract MPt22Si2-type compounds of the rare earth metals and Sr crystallize in the ThCr2Si2-type body-centered tetragonal structure. Structure factor calculations reveal that Pt and Si atoms are statistically distributed among their crystallographic positions. Interatomic distances were calculated and show relatively strong Si-Si bonds similar to the Cu-, Pd- and Au-containing ThCr2Si2-type compounds.

Low-temperature synthesis of metallic silicides and germanides by an amalgam method

Abstract Metallic silicides and germanides can be prepared at relatively low temperatures (400–500°C) by dissolving metal and silicon or germanium in mercury. Rare-earth disilicides and digermanides as well as suicides and germanides of Ni, Mn and Pt were prepared. The mechanism of the process is discussed.

Rare-earth silicides and germanides of the Mn5Si3 type substituted by europium

The substitution of europium atoms for other rare-earth metals in Ce5Ge3, Pr5Ge3, Gd5Ge3 and Gd5Si3 was studied. Results show that a maximum of one europium atom can be substituted in the above compounds without destroying their crystal structure. Crystal and Gd155 Mossbauer measurements were used to study the effect of europium.

Lead and strontium phosphate apatites substituted by rare earth and silver ions

Abstract Rare earth and silver substituted apatites of the M 10 − 2 x Ln x Ag x (PO 4 ) 6 Y 2 (M ≡ Sr and Pb; Ln ≡ La, Nd and Eu; Y ≡ F and Cl; x = 1 and 2) systems were prepared and studied by powder X-ray diffraction. The compounds crystallize in the apatite-like hexagonal P6 3 m structure. The substitution process in the Pb and Sr systems is discussed in view of the lattice parameter changes, the c a ratios, and the polarizing properties of the ions.