Shoichiro Nomura

DIELECTRIC PROPERTIES OF LEAD-STRONTIUM TITANATE

The dielectric and thermal properties and lattice dimensions of lead·strontium titanate were investigated, the solid solution being realized in the whole range of molar percentage. It was found that, lead·strontium titanate is also ferroelectric as lead·barium titanate and barium·strontium titanate. As the content of Sr 2+ increases, the lattice volume and tetragonality decrease. The Curie temperature decreases linearly with the increase of the content of Sr 2+ and any other transition point was not observed. Curie-Weiss formula holds above Curie temperature, the value of Curie constant being (3∼9)×10 4 °C.

Some Experimental and Theoretical Studies of Ferroelectricity in NaNO2

The dielectric constant of NaNO 2 crystal was measured in a temperature range from r.t. to 200°C and in a frequency range from 60 to 10 6 cycles per second. It shows peak at 164.2°C in heating and at 162.6°C in cooling. Dielectric dispersion, similar to the one observed in other ferroelectrics, exists in all directions of the crystal principal axes in the paraelectric region as well as in the ferroelectric one. The spontaneous polarization was determined by the measurement of the pyroelectric current and the value was estimated to be ca 8.6 µC/cm 2 at r.t.. The ferroelectricity in NaNO 2 was discussed in a phenomenological way, where the electrocaloric effect was taken into account. The free energy F was expressed as a function of the polarization P as F = A ( T - T 0 ) P 2 + B P 4 + C P 6 , and the coefficients were determined by the dielectric properties as A =1.22×10 -3 °K -1 , B =-0.3×10 -10 esu, C =1.0×10 -19 esu and T 0 =436.2°K. From the dielectric measurements, it is concluded that the transition ...

Domain Structure of NaNO2

The 180° domains along the b direction in NaNO 2 single crystals were observed by the etching method at room temperature. The domain boundaries lie parallel to (100). The virgin crystal prepared from the aqueous solution is almost of single-domain, but, after having once been heated above the Curie temperature, it has nearly the same domain structure as the crystal prepared from the melt. These domains were ascertained to be the ferroelectric ones from experiments with d c field. By the alkali etchant the positive end of the domain was more rapidly etched than the negative one, and nearly the contrary result was obtained for the acid etchant. The fact that the domain boundaries lie parallel to (100) would be intimately related with the thermal motion of NO 2 - radicals.

Dielectric Behavior of KNO3 in Its Ferroelectric Phase III

The dielectric behavior of KNO 3 crystal was investigated. Mainly in its ferroelectric phase III, which appears in the temperature range of about 125∼115°C on cooling, the D - E hysteresis loop along the c axis was observed by the usual Sawyer-Tower method using the 50 c/s a c electric field, the pyroelectric current in this direction was measured by the usual galvanometer method and the dielectric constants along the three crystal axes were measured by a C-meter using the 100 kc/s a c voltage. From the obtained results, the ferroelectricity in the phase III was discussed in relation with the motion of NO 3 groups.

Thermal Properties of NaNO2

Specific heat and thermal expansion coefficients of NaNO 2 crystal were measured from room temperature to 210°C. A conduction-type calorimeter was adopted for the measurement of the specific heat and a differential-type dilatometer for the measurement of the thermal dilatation. A λ-type anomaly in specific heat was observed near the transition temperature, the transition heat being calculated as ca 285 cal/mol. The crystal expands in the a and b direction, while it contracts in the c direction with increasing the temperature, and further the transition is accompanied by abrupt changes in the cell dimensions. Our results on thermal dilatation were compared with the ones obtained from the x-ray data. Ferroelectricity in NaNO 2 was discussed in connection with our results on thermal properties.

Dielectric Properties of Titanates Containg Sn4+ Ions I

Dielectric and thermal properties and lattice constants of the solid solutions of Pb(Ti·Sn)O 3 and Ba(Ti·Sn)O 3 were investigated, for the purpose of making clear the role of Y ion in the compounds of the perovskite type, XYO 3 . In Pb(Ti·Sn)O 3 , according to the X-ray analysis, two phases seem to co-exist in the samples containing Sn 4+ ions more than 75%, although the whole range solid solution might be expected from the standpoint of the “tolerance factor”. The Curie point moves to the low temperature side with the increase of the content of PbSnO 3 and reaches 200°C in Pb(20%Ti·80%Sn)O 3 . In Ba(Ti·Sn)O 3 , a rather steep decrease of the Curie temperature with the content of Sn 4+ ions occurs and the whole range solid solution seems to be realized, although the X-ray analysis was not thoroughly made in this case. The dielectric constant D ∼ E hysteresis loop, thermal expansion and specific heat were observed. An anomalous hysteresis phenomenon was observed in Pb(25%Ti·75%Sn)O 3 , which suggests that ...

Phase Transition in Sr(NiW)0.5O3-Ba(NiW)0.5O3 System

Crystal structures, electrical and magnetic properties of Sr(NiW) 0.5 O 3 -Ba(NiW) 0.5 O 3 system were studied in the temperature range from room temperature to about 400°C. The compound of strontium undergoes a phase transition at about 260°C, where the crystal structure which is perovskite-like changes from tetragonal to cubic. The anomaly was also observed at the transition temperature in the measurements of electrical and magnetic properties. Sr(NiW) 0.5 O 3 shows a rather small value of dielectric constant of about 17 and the magnetic susceptibility of 6.2×10 -6 e.m.u. at room temperature. Ba(NiW) 0.5 O 3 which is cubic in the whole range shows the similar values. Both substances behave as paramagnetic, though a small anomaly is observed in Sr(NiW) 0.5 O 3 at the tetragonal-cubic transition. The effective Bohr magneton numbers of Ni 2+ are estimated as 2.92 in the tetragonal and 3.06 in the cubic for Sr(NiW) 0.5 O 3 and 3.02 for Ba(NiW) 0.5 O 3 . The lattice distortion observed in the compound of str...

Solid State Reaction between Barium Titanate and Strontium Titanate

The first stage of the sintering process between barium titanate and strontium titanate powders, which are responsible for the formation of solid solution, was investigated. We measured the variation of permittivity vs . temperature characteristics and crystal structure of the mixtures, with sintering conditions. The shift of the effective Curie temperature and the broadening of diffracted lines were observed in the transient states of the reaction. A diffusion mechanism was introduced in order to interpret these phenomena qualitatively.