Noriyuki Kohzu

The effect of rare-earth (La, Sm, Dy, Ho and Er) and Mg on the microstructure in BaTiO3

Abstract The effect of rare-earth elements, La, Sm, Dy, Ho and Er, on the microstructure in BaTiO3(BT)–MgO–rare-earth oxide based system was studied. Larger amount of MgO was required to suppress the grain growth for the larger ionic radius rare-earth ion (La, Sm)-doped samples than for the smaller ion (Dy, Ho, Er)-doped samples. Also, substitution modes of rare-earth elements and Mg in BT lattice were investigated. The solubility of rare-earth ions in BT lattice and the substitution ratio of rare-earth ions into Ba-site decreased as ionic radius decreases. This suggests that the formation of core-shell structures in BT–MgO–rare-earth oxide based system is dependent on the substitution ratio of rare-earth ions into Ba-site.

Occupational sites and dielectric properties of rare-earth and Mn substituted BaTiO3

Abstract The effect of re-oxidation treatment on the solubility in dopants and the dielectric properties of La–Mn- and Ho–Mn-substituted BaTiO 3 ( AB O 3 ) was investigated. The lattice parameter and electrical resistivity results indicated that La ions occupied A -sites and Ho ions occupied both A - and B -sites. In the case of Ho–Mn-substituted samples, the decrease in lattice parameter and a shift of the Curie point ( T c ) to higher temperatures by re-oxidation treatment were observed in the range in which Ho ions predominantly occupy B -sites (act as acceptors). On the other hand, La–Mn-substituted samples showed little change. Electron spin resonance measurements revealed that these changes due to re-oxidation were based on the decrease of the ionic size of Mn due to the oxidation of Mn 2+ to Mn 3+ or Mn 4+ . The occupational sites of Ho ions strongly affected the valence state of Mn and the dielectric properties of BaTiO 3 .

Studies on the Solid Solution of Mn in BaTiO3

BaTi1-xMnxO3 solid solutions with 0≤x≤0.04 were synthesized in reducing atmosphere (PO2<10-9 Pa) and in air at 1350°C for 2 h. The effect of Mn ions with different valences on the crystal structure of BaTiO3 was studied by the room-temperature Raman scattering, electron spin resonance (ESR) and X-ray powder diffraction analyses. The crystal structure of the solid solution was analyzed to determine the change of its lattice parameters. It was found that in a reducing atmosphere, Mn2+ ions promoted the tetragonal-to-cubic transformation, as both a contraction of c-axis and an extension of a-axis were observed with an increase in Mn content. In contrast, Mn ions in the air-synthesized samples promoted the tetragonal-to-hexagonal transformation. The formation of the hexagonal phase was accompanied by a strong extension of the c-axis of the tetragonal phase from 4.032 A to 4.042 A. This was attributed to Jahn-Teller distortions caused by Mn3+ ions.

INFLUENCE OF THE MICROSTRUCTURE EVOLUTION ON ELECTRICAL PROPERTIES OF MULTILAYER CAPACITOR WITH NI ELECTRODE

The influence of the microstructure evolution on electrical properties as a parameter of the firing temperature was studied for materials in the BaTiO3(BT)–MgO–Ln2O3 (Ln=Ho and Dy) system. The sintering behavior and the formation of the core-shell structure were dependent on the kind of doped rare earth elements. The stability of the core-shell structure and electrical properties of Dy doped specimens against the firing temperature were much lower than those of the Ho doped specimens. Especially, the Dy doped disk specimens fired at more than 1320°C, in which the core-shell grains were destroyed as judged by the differential scanning calorimetry (DSC) measurement and the transmission electron microscopy (TEM) observation, exhibited characteristic electrical properties. The electrical properties of the Ho doped multilayer capacitor (MLC) specimen were superior to those of the Dy doped one. It was found that the microstructure had a definite influence on the electrical properties, such as the temperature dependence of the dielectric constant and the capacitance aging behavior under an unloaded field.

Effect of Occupational Sites of Rare-Earth Elements on the Microstructure in BaTiO3

The effect of rare-earth elements such as La, Ho and Yb on the microstructure in BaTiO3 (ABO3) with various Ba/Ti ratios was studied. The grain size changed markedly depending on the Ba/Ti ratio in the case of La- and Yb-doped BaTiO3. On the other hand, in the case of Ho-doped BaTiO3, the grain size changed gradually in a wide range of Ba/Ti ratio. It is considered that Ho ions occupy both A- and B-sites, depending on the Ba/Ti ratio, while La and Yb ions occupy A- and B-sites, respectively. The solubility, the microstructure and the resistivity of rare-earth elements and Mg-substituted BaTiO3 were also investigated. It was also confirmed that La ions occupied A-sites, Yb ions occupied B-sites and Ho ions occupied both A- and B-sites. It appears that the drastic change of the resistivity of Ho–Mg-substituted BaTiO3 is due to the change in the predominant occupational site of Ho ions.

Study of Occupational Sites and Dielectric Properties of Ho-Mg and Ho-Mn Substituted BaTiO3.

The effect of re-oxidation treatment on the solubility in dopants and the dielectric properties of Ho–Mg- and Ho–Mn-substituted BaTiO3 was investigated. The lattice parameter and electrical resistivity results indicated that the predominant occupational sites of Ho ions changed from A-sites to B-sites by increasing the doped content in both systems. In the case of Ho–Mn-substituted samples, the decrease in lattice parameter and a shift of the Curie point (Tc) to higher temperatures by re-oxidation treatment were observed in the range in which Ho ions predominantly occupy B-sites (act as acceptors). On the other hand, Ho–Mg-substituted samples showed little change. Electron spin resonance measurements revealed that these changes due to re-oxidation were based on the decrease of the ionic size of Mn due to the oxidation of Mn2+ to Mn3+ or Mn4+. The occupational sites of Ho ions strongly affected the valence state of Mn and the dielectric properties of BaTiO3.

Effect of occupational sites of rare-earth elements on the Curie point in BaTiO/sub 3/

The relationship between the dielectric properties and the occupational sites of rare-earth ions in various rare-earth oxides and acceptors (Mg, Mn) substituted BaTiO/sub 3/ was investigated. In the case of La, Sm, Gd and Yb doped samples, T/sub c/ decreased almost linearly with increasing doped content On the other hand, in the case of Dy, Ho and Er doped samples, T/sub c/ decreased in two stages. Furthermore, (Dy, Ho, Er, Yb)- and Mn-substituted samples showed the T/sub c/ shift by re-oxidation treatment, while (La, Sm)- and Mn-substituted samples showed no change. It was confirmed that the behaviors of the T/sub c/ shift were due to the change in predominant occupational site of rare-earth ions in BATiO/sub 3/ lattice.