Crystal structure and properties of valleriite

Valleriite is a relatively rare and unusual mineral, displaying a regular stacking of sulphide and hydroxide layers. The combination of two such entirely different building units is a peculiarity in several ways. Since the structural topology of the two layers is different, they only match conditionally in certain directions. Thus a regular alternating of the two different structures develops. Such materials are known as composite - crystals, a description of the atomic structure takes place in the multidimensional (3+n) space. Within the group of sulphides such composite - and also incommensurably modulated structures occur quite frequently and represent current research trends in modern crystallography. In addition the physical properties of valleriite and derived synthetic compounds promise to be of interest: it is the combination of the n-type semi-conducting chalcopyrite-type layer with the hydrogen and transition metal containing brucite layer which makes the material of interest, especially with respect to photo-electrochemical properties; a technical application may be possible. However, even basic physical properties of valleriite are unknown. The aim of the proposed research project is a comprehensive chemical and structural as well as a fundamental physical characterisation of natural and synthetically manufactured valleriite type materials. The determination of the parameters (P - T - X and fugacity) important for the synthesis of phase pure and well crystallized samples represents thereby an important project emphasis.

Valleriite is a relatively rare and unusual mineral, displaying a regular stacking of sulphide and hydroxide layers. The combination of two such entirely different building units is a peculiarity in several ways. Since the structural topology of the two layers is different, they only match conditionally in certain directions. Thus a regular alternating of the two different structures develops. Such materials are known as composite - crystals, a description of the atomic structure takes place in the multidimensional (3+n) space. Within the group of sulphides such composite - and also incommensurably modulated structures occur quite frequently and represent current research trends in modern crystallography. In addition the physical properties of valleriite and derived synthetic compounds promise to be of interest: it is the combination of the n-type semi-conducting chalcopyrite-type layer with the hydrogen and transition metal containing brucite layer which makes the material of interest, especially with respect to photo-electrochemical properties; a technical application may be possible. However, even basic physical properties of valleriite are unknown. The aim of the proposed research project is a comprehensive chemical and structural as well as a fundamental physical characterisation of natural and synthetically manufactured valleriite type materials. The determination of the parameters (P - T - X and fugacity) important for the synthesis of phase pure and well crystallized samples represents thereby an important project emphasis.