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Twinning and de twinning in calcite were studied by means of selective etching and sound-attenuation measurements in order to investigate dislocation behavior during these processes. Twinning was accompanied by an increase in attenuation caused by discontinuous dislocation multiplication in the twin lamella. During de twinning the attenuation changes were recovered by dislocation cluster formation and tangling. It was found that dislocation nucleation accompanies even elastic twinning in calcite and is probably responsible for various anelastic effects associated with it.

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The hole-concentration (x) dependence of the three-dimensional energy-momentum dispersion in (Bi, Pb)2(Sr, La)2CuO(6+delta) has been investigated by angle-resolved photoemission spectroscopy. For a heavily overdoped sample of T(c) < or = 0.5 K, an energy dispersion of approximately 10 meV in width is observed in the vicinity of the (pi, 0) point with varying momentum along the c axis (k(z)). This k(z) dispersion is zero for underdoped, optimally doped, and slightly overdoped samples up to a doping level corresponding to T(c) = 22 k. At higher doping levels we observe significant dispersion of the order of 10 meV (sample with T(c) < or = 0.5 K). This is clear evidence that at a doping value corresponding to T(c) = 22 K, a crossover from two- to three-dimensional electronic structure occurs.