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Raman scattering is used to investigate the oxygen-octahedral [A.sub.1g](O) phonons for both 1:2 ordered xBaTi[O.sub.3](1-x)Ba([Mg.sub.1/3][Ta.sub.2/3])[O.sub.3] and 1:1 xCa([Sc.sub.1/2][Nb.sub.1/2])[O.sub.3](1-x)Ba([Sc.sub.1/2][Nb.sub.1/2])[O.sub.3] ceramics. The size and the atomic polarizability of doped atoms and the substitution site have affected the phonon properties of the oxygen octahedral structure.

Oxygen-octahedral A1g(O) phonons for both 1:2 ordered xBaTiO3+(1-x)Ba(Mg1/3Ta2/3)O3 (0≤x≤ 0.05) and 1:1 ordered xCa(Sc1/2Nb1/2)O3+(1-x)Ba(Sc1/2Nb1/2)O3 (0≤x≤ 0.25) ceramics were investigated using Raman scattering. Lineshapes of A1g(O) phonons directly reflect structural characteristic of TiO6, TaO6, ScO6, and NbO6 octahedral cages that are strongly correlated with microwave performance of the samples. The larger width of stretching A1g(O) phonon, implies poor crystalline structure and short phonon lifetime, giving us lower value of Q×f. The atomic polarizabilities of Ta5+, Ti4+, Ca2+, Sc3+, and Nb5+ have a strong influence on the structure of oxygen octahedron that dominates microwave performance of xBaTiO3+(1-x)Ba(Mg1/3Ta2/3)O3 and xCa(Sc1/2Nb1/2)O3+(1-x)Ba(Sc1/2Nb1/2)O3 ceramics. [ABSTRACT FROM AUTHOR]

Hydrothermally synthesized barium titanate, BaTiO3 (commercially available), has internal pores in small particles. The three-dimensional structures of the pores were successfully observed using transmission electron microscopy (TEM) and reconstructed by a tomography system. The behavior of the internal pore is observed in situ with increasing temperature on the thermal stage of a TEM device. We succeed in recording the movement of pores and small grains. At >1128 K, some pores move out from the particle's surface during TEM observation. The temperature roughly agrees with the temperature at which the density of BaTiO3 powder sharply increases. During observation with increasing temperature, a thin layer appeared on the particle's surface at >73 K and then disappeared at 1193 K. [ABSTRACT FROM AUTHOR]

The products and microwave dielectric properties of ceramics with nominal composition (Ba0.9Ca0.1)(YxB′1/2)O(3x+4.5)/2 (B′=Nb5+, Ta5+) are investigated. When x=0.5, i.e. (Ba0.9Ca0.1)(Y1/2B′1/2)O3 (B′=Nb5+, Ta5+), the product contains a considerable amount of Y2O3 as well as the main perovskite phase. When x=0.3 the product is single phase, equivalent to Ba(Ca1/9Y3/9Nb5/9)O3 or Ba(Ca1/9Y3/9Ta5/9)O3. The lattice parameters of these new compounds are smaller than those of Ba(Y1/2Nb1/2)O3 and Ba(Y1/2Ta1/2)O3. The relative permittivities (ϵr) of these new compounds are larger than those of Ba(Y1/2B′1/2)O3 (B′=Nb5+, Ta5+). The increase in ϵr of the Nb-system is about 4 times larger than that of the Ta-system. The Q f values of the present ceramics are larger than the Ca-containing perovskite in the (Ba1−xCax)(Mg1/3Ta2/3)O3 system. The sharp increase of ϵr in this study cannot be explained by the Ca2+ rattling ion model at the A-site, which applies to the case of the (Ba1−xCax)(Mg1/3Ta2/3)O3 system. A new method to explain the increase in ϵr is discussed. [Copyright &y& Elsevier]

The products and microwave dielectric properties of ceramics were investigated which had nominal composition (Ba1−xCax)(B1/2B1/2′)O3 (B3+=Y3+, Nd3+, Gd3+; B′5+=Nb5+, Ta5+). The products versus x relationships of these systems were complex, owing to the small amounts of the third and fourth compounds in a wide range of intermediate x. Dielectric properties of (Ba1−xCax)(Nd1/2Nb1/2)O3, (Ba1−xCax)(Y1/2Nb1/2)O3 and (Ba1−xCax)(Y1/2Ta1/2)O3 systems were evaluated. Relative permittivities (ϵr) of the first system changed linearly with x; however, those of the last two systems increased sharply to have respective peaks at x of 0.2, and then decreased with x. Those sharp increases in ϵr were similar to those reported for (Ba1−xCax)(Mg1/3Ta2/3)O3 and other systems. However, the relative values of the increase in ϵr were different. Plausible mechanisms to explain those differences among systems are discussed by introducing an index of rattling of the Ca2+ ion. [Copyright &y& Elsevier]