Contraction (density increase) and stress build-up in borosilicate glasses by ultra-violet irradiation were reported by the authors (J. Ceram. Asso. Japan, 72 [11-1] 193 (1964)). Experiments were carried out to check on correlation between these phenomena and some electronic process (formation of colour center or space charge, accumulation of luminescence and their thermal release) caused by irradiation.
Three groups of glass samples were examined with the results described below:
1. Six kinds of commercial glasses were irradiated by Co⁶⁰ gamma ray with total dose of 7×10⁷r. In spite of distinct blackening density change was not recognized. Thermoluminescence was intense in fused silica, while not recognized in lead glasses.
2. Outer protection bulb (soda borosilicate glass) of a mercury discharge lamp damaged by ultra-violet irradiation showed stress at inner surface and colouring, and by heating bleaching, thermoluminescence and release of space charge took place. These proved that the damage was not a result of thermal effect such as overheating.
3. Two kinds of commercial borosilicate glasses were irradiated by 400W mercury discharge lamp for two weeks or by Co⁶⁰ gamma ray with total dose of 5×10⁷r. In the former ones, though colouring and thermoluminescence were slight or unrecognized, stress build-up at irradiated surfaces was observed. In the later ones, distinct blackening and thermoluminescence were observed.
Interaction between ultra-violet ray and glass and related problems were discussed. Temperature ranges in which various thermal release phenomena took place were compared. Following the authors' opinion, contraction of glass by ultra-violet irradiation seemed not to directly related with electronic phenomena. Strictly speaking, however, this is still an open question. Moreover, the possibility of triggering or catalytic actions of electronic processes is a problem to be studied in future.

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Between the titanium spinels with the composition of xCoO⋅(2-x)MgO⋅TiO₂ and xCoO⋅(2-x)ZnO⋅TiO₂, remarkable difference of the color development is observed, especially in Co²⁺ ions poor region. The former is bluish green, and the latter brown. The same phenomenon is observed between the other spinels with the composition of xCoO⋅(1-x)NiO⋅MgO⋅TiO₂ and x CoO⋅(1-x)NiO⋅ZnO⋅TiO₂, namely, the former bluish green and the latter greyish or brownish green. This is due to the strong tetrahedral preference of Zn²⁺ ions, as the result of which Co²⁺ ions become absent from tetrahedral interstices in the spinels of x CoO⋅(2-x)ZnO⋅TiO₂ and x CoO⋅(1-x)NiO⋅ZnO⋅TiO₂.
To observe the influence of the preference of each cation such as Mg²⁺, Zn²⁺, Co²⁺ and Ni²⁺ upon the spinel formation and the color development, the gradual substitution of Zn²⁺ for Mg²⁺ in the spinels of CoO⋅MgO⋅TiO₂, NiO⋅MgO⋅TiO₂ and CoO⋅NiO⋅MgO⋅TiO₂ systems was carried out. The components were mixed by wet, calcined. at 1300°C for one hour. The reflectance between 400-760mμ was measured by a selfrecording photoelectric spectrometer to represent the result by C. I. E. color specification, and X-ray analysis was carried out to observe the spinel formation and to calculate the lattice constant. The results were summarized as follows.
1. CoO-MgO-ZnO-TiO₂ system.
The spinels with the composition of 0.2CoO⋅(1.8-x)MgO⋅xZnO⋅TiO₂, 0.5CoO⋅(1.5-x)MgO⋅xZnO⋅TiO₂ and CoO⋅(1-x)MgO⋅xZnO⋅TiO₂ were prepared. The absorption of tetrahedral Co²⁺ ion was observed, and a deep absorption ranging about 550-680mμ, characteristic of it, was also revealed when x=0. But with increasing the amount of x, this deep absorption diminished, and a new absorption about 530mμ due to octahedral Co²⁺ ion appeared. The color became bluish green to brown at the composition in which the tetrahedral Mg²⁺ ions were completely replaced by Zn²⁺ ions. For example, in 0.5CoO⋅(1.5-x)MgO⋅xZnO⋅TiO₂, the substitution proceeded as follows;
Co_0.5Mg_0.5[MgTi]O₄→Co_0.5Zn_0.5[MgTi]O₄→Zn[Co_0.5Zn_0.5Ti)O₄ (the bracket represents octahedral interstices). This substitution was reflected in the lattice constant too.
2. NiO-MgO-ZnO-TiO₂ system
The spinels with the composition of 0.2NiO⋅(1.8-x)MgO⋅xZnO⋅TiO₂ and NiO⋅(1-x)MgO⋅xZnO⋅TiO₂ were prepared. According to Romeijn, Dunitz et al., Ni²⁺ ion has the strong octahedral preference, and in most cases does not occupy tetrahedral interstices owing to its electron configuration d⁸. In this case Ni²⁺ ions occupy octahedral interstices continually. Therefore, there is no difference in color development between the spinels in NiO-MgO-TiO₂ and NiO-ZnO-TiO₂ systems. NiO⋅MgO⋅TiO₂ did not form the spinel structure owing to the difficulty of distribution of cations among tetrahedral and octahedral interstices in the spinel lattice. (Ni²⁺ and Ti⁴⁺ ions have octahedral preference, and Mg²⁺ ion is expected to be the same, because MgO is of

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The purpose of this study is to clear the sintering process of raw powders of ceramic dielectric materials by hot pressing and the electrical property of hot pressed ferroelectric ceramics.
The results obtained are summarized as follows.
(1) At first, systematic experiments were carried out on the variation of the apparent density (ρ) in the sintering process of the following solid reaction,
Bi₂O₃+3ZrO₂→Bi₂(ZrO₃)₃…(1)
As a function of the maximum firing temperature (T_m), the hot pressing pressure (P_h) and the duration of the hot pressing (t_p) in the temperature range from room temperature to the temperature when the material turns into dense ceramic body.
When the mixture of raw powders of the equation (1) was heated by ordinary firing method, the value of ρ increased from about 700°C and the sintering was completed at about 900°C. When P_h was applied, the above solid reaction was promoted above 500°C and ρ-T_m curves were shifted to lower temperature side according to the value of P_h. The density of the ceramic body prepared by hotpressing under the condition T_m=800°C, P_h=1000kg/cm² and t_p=30min, was higher than that prepared by ordinary firing at 900°C for 1hr. Next, the relation between the porosity (p) of the hot-pressed ceramics and t_p at constant T_m and P_h was examined.
(2) The same experiments were made on the following solid reaction,
0.94PhO+0.06SrCO₃+0.53ZrO₂+0.47TiO₂
→Pb_0.94Sr_0.06(Zr_0.53-Ti_0.47)O₃…(2)
In the sintering process of the equation (2) by ordinary firing method, anomalous expansion was observed at 500°-600°C. We examined ρ-T_m curves under the constant pressures, P_h=100, 300 and 700kg/cm². Consequently, the degree of the anomalous expansion was decreased by hot-pressing. At P_h of 300kg/cm², slight anomalous expansion was observed. Furthermore, the anomalous expansion was not observed at P_h of 700kg/cm² and the apparent density increased at above 600°C. According to the above experiments, it can be assumed that the pressure to prevent the reduction of density (P_a) is about 400-500kg/cm². This value seems to be useful to discuss the cause of the anomalous expansion. The density of the specimens prepared by hot-pressing under the condition T_m=900°C, P_h=700kg/cm² and t_p=30min was 7.6g/cm³ and this value is the same as that prepared by ordinary firing at 1300°C for 1hr in the PbO atmosphere.
(3) The dielectric property in the temperature range 0°-400°C was examined on several specimens of (Pb-Sr) (Zr-Ti)O₃ prepared by various methods. The specimens prepared by ordinary firing showed the sharp Curie peak at 310°C. The specimens prepared by hot pressing showed the flat temperature dependency of permittivity. After annealing the hot-pressed ceramics at higher temperature, the variation of dimension was measured in the direction of thickness and radius. Consequently, it was found that the ceramic body sintered by hot-pressing has a considerable residual strain in the thickness direction and this residual strain was released by annealing.
The value of the permittivity at Curie temperature was increased by annealing. The existence of the residual strain in the hot-pressed ceramics was also supported by the X-ray diffraction pattern.

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