The effects of Dy doping and sintering parameters on the properties of BaTiO3 ceramics were studied. The average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy. The Curie temperature change, associated with ≤1.2 at.% Dy, is <3°C. The dielectric constant is ∼2600 for specimens doped with 0.8 at.% Dy, calcined at 1200°C, and sintered at 1450°C. The dielectric constant variation with ambient temperature is much less than that of conventional BaTiO3 ceramics. Lattice constant c decreases with increasing Dy concentration whereas a increases slightly. The effects of grain size on dielectric constant, lattice parameters, and linear thermal expansion coefficient are more pronounced than the chemical effects of Dy doping in the ferroelectric state, whereas in the paraelectric state, these characteristics are almost independent of grain size as well as Dy concentration. The decrease in the frequency of occurrence of 90° twins with decreasing grain size implies that internal stress, which develops when BaTiO3 ceramics are cooled below Tc, strongly influences the effects of grain size.
YBa2Cu3O7+y
samples, slowly cooled after annealing, are orthorhombic and exhibit a complete transition at 90 K. On the contrary, rapidly quenched samples are tetragonal and their T
c's are 20 K lower than those of the slowly cooled ones. It is found from thermogravimetric analysis that the amount of oxygen deficiency in the tetragonal samples is greater than the orthorhombic ones. This fact indicates that the structural difference is attributed to both the disordering of oxygen vacancies and the difference in oxygen vacancy amount. In addition, YSr2Cu3O7+y
samples are tetragonal and exhibit complete transition at 81 K.
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