We have revealed new features in the out-of-plane resistivity ρc of heavily underdoped RBa2Cu3O6+x (R=Tm,Lu) single crystals, which give evidence for two distinct mechanisms contributing the c-axis transport. We have observed a crossover towards "metal-like" (∂ρc/∂T > 0) behavior at the temperature Tm which quickly increases with decreasing doping. The "metallike" conductivity contribution dominates at T < Tm and provides a saturation of the resistivity anisotropy, ρc/ρ ab . The antiferromagnetic ordering is found to block this "metal-like" part of the c-axis conductivity and complete decoupling of CuO2 planes, which may be the reason of superconductivity disappearance.

Glauconites are dioctahedral, microdivided, Fe-containing silicates whose idealized structure may be described as a stacking of 2 : 1 layers with the same azimuthal orientation. The diffractometric and crystallochemical data do not coincide with this idealized structural model. For each glauconite studied the best fit between experimental and theoretical XRD patterns was obtained using the same model. It was possible to describe the stacking by an equally probable occurrence of layers rotated by multiples of 60°. The layer types alternate with a definite tendency to segregation. The model is characteristic for all glauconites, irrespective of composition, age and type of host rock. The alternation of layers rotated by 60° in the structure leads to both octahedral and prismatic coordination for the interlayer K+ cation.

No abstract

No abstract

No abstract