The aim of the r-licrosyPlposium is to dis-

Different degrees of similarity between inorganic crystal structures are defined concisely and examples are presented that illustrate their practical application. A notation giving the coordination of atoms is presented together with some basic rules for developing crystal-chemical formulae and the Bauverband description of inorganic structure types. Typical examples of the nomenclature are: pyrite Fe[6°]{g}[S2 (3;1)t ], [F(□2l) + F′FeS2Pa\bar 3; spinel Mg[4]AI2 [6]O4, ∞ 3[Mg[4t]lAl2 [6o]O4 [l,3;12co]], Fm 222 + D, T′ MgAI2O4 Fd\bar 3m.

HermannBraune zum 60. Geburtstag gewidmet Zur Erweiterung der Kenntnis über das chemische Verhalten des Galliums und Indiums in Legierungen wurde eine größere Anzahl bislang unbekannter (20) Kristallstrukturen intermetallischer Phasen dieser Elemente mit Übergangselementen bestimmt. Unter den gefundenen Typen sind solche bevorzugt, die vom geometrischen Standpunkt aus (wegen der atomaren Abstandsverhältnisse) das Wirken heteropolarer Kräfte erkennen lassen. Die Ergebnisse bestätigen die Annahme heteropolarer Bindungstendenzen, die in diesen Systemen als Ausdruck eines elektronegativen Charakters von Gallium und Indium anzusehen sind.

No abstract

Magnetisation measurements of three synthetic single-crystals A2SiO4 of the olivine family are presented (A=Mn, Fe and Co). All three compounds order antiferromagnetically in the range 45-65 K. For A=Mn, weak ferromagnetism is present. For A=Fe and Co, the magnetisation is strongly anisotropic. A model is proposed, which extends existing published explanations of the magnetic structures. The magnetic cations are represented by spin Hamiltonians, and their interactions by mean fields. Analytical relationships are derived between Curie temperatures, Curie constants and Neel temperatures on the one hand, and spin Hamiltonian parameters on the other. From the latter parameters the maximum possible information on orbital levels is derived. This is enough to calculate magnetic entropies in good agreement with published data, together with specific heat measurements, and to point out the limits of validity of the linearisation processes that are necessary to obtain usable analytical relations between experimental and atomic parameters. Below TN, the susceptibilities are analysed using the conclusions of previous magnetic structure studies, especially those concerning the role of competing exchanges, single-ion anisotropies, and symmetry requirements.