Schottky Anomalies in the Low-Temperature Specific Heat of YBa.sub.2Cu.sub.3O.sub.y HTSC

The evolution of the Schottky anomalies in the temperature dependence of the specific heat (in the temperature range T = 2-10 K and the magnetic field range H = 0-9 T) of polycrystalline YBa.sub.2Cu.sub.3O.sub.y HTSCs is studied when the oxygen content in coarse-crystalline samples changes and when the degree of structural disordering in optimally doped fine-crystalline samples of the same compound changes. The number of paramagnetic centers with uncompensated spin moments, which generate the Schottky anomalies, and the splitting of the lower energy levels are estimated. A correlation between these parameters and both the number of oxygen vacancies in chain planes and the method of oxygen ordering in chains is found. The experimental data are compared with the results of studying the magnetic susceptibility at T > T.sub.c in the same samples. Based on this comparison, we can conclude that the nature of the Schottky centers is related to the formation of paramagnetic centers at breaks in the Cu1-O4 copper-oxygen chains in the basal planes of the crystal structure.