Crystal-field effects are very important as far as laser performances of Yb-doped materials are concerned. In order to simplify the interpretation of low-temperature spectra, two tools derived from a careful examination of crystal-field interaction are presented. Both approaches are successfully applied in the case of new Yb-doped materials, namely Ca3Y2(BO3)4 (CYB), Ca3Gd2(BO3)4 (CaGB), Sr3Y(BO3)3 (SrYBO), Ba3Lu(BO3)3 (BLuB), Y2SiO5 (YSO), Ca2Al2SiO7 (CAS) and SrY4(SiO4)3O (SYS). The 2F7/2 splitting is particularly large in these materials and favourable to a quasi-three-level laser operating scheme. Calculations performed using the point charge electrostatic model for these compounds and using a consistent set of effective atomic charges confirm the experimental results. This should permit to use this model in a predictive approach.

A structural model is proposed to explain the abnormal broadening of the (10ℓ) and (20ℓ) lines in the X‐ray diffraction pattern of nickel hydroxide. This model, based on a hypothesis of the presence of stacking faults, allows us to rationalize the empirically established relationship between the presence of such peculiarities in X‐ray diffraction patterns and the good electrochemical behavior of the material. Two types of stacking faults, i.e., growth and deformation faults, corresponding to the existence within the hexagonal oxygen packing of one or two face‐centered cubic oxygen sequences, respectively, have been identified. The simulation, with the DIFFaX program, of the X‐ray diffraction patterns of nickel hydroxide samples has allowed us to determine in a general way the nature and the amount of stacking faults. It is shown that the stability of protons in tetrahedral sites depends on whether they are in the vicinity of a stacking fault or not, and this explains the improvement of both the chargeability of the material and its electronic conductivity in the presence of defects. It is shown as well that stacking faults in the electrochemically active material lead to a more facile transition to the γ phase during overcharge in concentrated electrolyte. © 1999 The Electrochemical Society. All rights reserved.