Piezoelectric properties of high Curie temperature barium titanate-bismuth perovskite-type oxide system ceramics

Barium titanate (BaTiO3, BT)-bismuth magnesium titanium oxide [Bi(Mg0.5Ti0.5)O-3, BMT] system ceramics were prepared in an ambient atmosphere in order to increase the Curie temperature (T-c) of BT above 132 degrees C. A single perovskite phase was observed for BT-BMT ceramics with BMT compositions less than 50 mol %, and their relative densities were greater than 94%. Synchrotron measured x-ray diffraction patterns revealed that all the cations in the ceramics were homogeneously distributed. The temperature dependence of the dielectric properties revealed that the BT-BMT system ceramics exhibited relaxorlike characteristics with a dielectric maximum temperature as high as 360 degrees C for the 0.5BT-0.5BMT ceramic. The apparent piezoelectric constant (d*) was 60 pC/N for the 0.4BT-0.6BMT ceramic. Based upon these results, the BT-BMT system shows potential as a new type of lead-free material for high T-c piezoelectric applications

Effects of pressure on organic reactions V : the base-catalyzed decomposition of diacetone alcohol in two aqueous alcohol mixtures

The effects of solvent and pressure on the rate of the base-catalyzed decomposition of diacetone alcohol have been measured in two aqueous mixtures involving methanol and isopropanol at 20.00～40.00℃, and in aqueous methanol at 30.00℃, respectively. The constant-pressure activation parameters for the decomposition in various compositions of solvent exhibit that ΔG_P≠ is slightly dependent on the solvent composition but oppositely in the direction due to the solvent system, whereas ΔH_P≠ and ΔS_P≒ in both systems increase in a compensating manner as the content of alcohol rises, having no minima. The activation volume obtained in the methanol system increases also simply without any minimum against the solvent axis. These results are discussed in comparison with those of the ethanol system studied previously

Effects of pressure on organic reactions IV : the base-catalyzed decomposition of diacetone alcohol in aqueous ethanol mixtures

The effects of solvent and pressure on the rate of the base-catalyzed decomposition of diacetone alcohol in aqueous ethanol mixtures have been measured at 20.00～40.00℃ and at 30.00～40.00℃, respectively. The variation with solvent composition of the activation parameters ΔG_P≠, ΔH_P≠ and ΔS_P≠ at constant pressure indicates that ΔG_P≠ gives only a slight solvent dependence compared with ΔH_P≠ and ΔS_P≠, so shat the latter two parameters vary vary with solvent composition in a compensating manner given by δΔH_P≠ = βδΔS_P≠. The β-value seems to be strongly dependent on the acidity of organic cosolvent. The small minima observed in ΔH_P≠ and ΔS_P≠ in highly aqueous region may be mainly attributed to relatively large change of internal pressure in the solvent system, which will reflect an increase in its structuredness by small addition of organic cosolvent to water. The activation volume exhibits also the minimum behavior similar to those in ΔH_P≠ and ΔS_P≠, and changes the sign from negative to positive as the temperature rises. From these results, it is reasonably suggested that in highly aqueous solvents a water molecule at least is incorporated into the transition state and that the cleavage of carbon-carbon bond of the reaction species in the slow step is accompanied rather than followed by the hydrogen abstraction from a water molecule lending to the formation of products

The effect of pressure and temperature on the base-catalyzed condensation of cyclohexanone (The co-operative researches on the fundamental studies of the liquid phase reactions at high pressures)

The base-catalyzed condensation of cyclohexanone to ketol in ethanol solution has been kinetically investigated in the range 0.68～9.75℃ and 1～2, 000kg/cm^2. The activation energy and entropy at 1 atm are 12.7 kcal/mole and -33.1cal/deg・mole, which are both quite close to the results in the absence of the solvent. The activation volume is -7.4cm^3/mole at 0.68℃ and -7.8 cm^3/mole at 9.75℃. From these results, it may be reasonably concluded that the transition state is not so much polar and the acceleration of a reaction can be mainly attributed to the structural effect

Effects of pressure on organic reactions II : the acid-catalyzed rearrangement of pinacol

The effect of pressures up to 1, 447 bar on the rate of the acid-catalyzed rearrangement of pinacol bas been measured at 60～70℃ in dilute hydrochloric acid and at 25℃ in concentrated sulfuric acid. The volumes of activation in the former at 1 bar are in the range from 6.8 to 8.4 cm^3/mole, and decrease as the temperature rises. The energy and entropy of activation at 1 bar are 36.1kcal/mole and 22.3 cal/deg・mole, respectively, and both increase with increasing pressure. On the other band, the volume of activation in the latter at 1 bar is 6.1 cm^3/mole in 47.5 wt% and 5.6 cm^3/mole in 55.8 wt%' sulfuric acid. A modified mechanism for the rearrangement has been discussed in the light of these results. Consequently, it is suggested that the slow step is the migration of the methyl group of the intermediate ion (R...OH_2)^+ formed from the protonated pinacol and is not probably varied with the acidity of the solution