Yoshitaka Somiya

Study of (Sr, Pb)TiO3 ceramics on dielectric and physical properties

Abstract (Sr 1− x Pb x )TiO 3 ( x =0.2, 0.25 and 0.3) ceramics were prepared by the conventional mixed oxide method. Their dielectric permittivity, and loss tangent values were measured with and without DC bias field, thermal expansion and microstructure were observed. Three compositions showed similar Curie–Weiss constant, ca. 1×10 5 °C and thermal expansion coefficient, 10×10 −6 °C −1 . Transition temperatures of the compositions were, −60, −25 and 10°C, respectively, with loss tangent values of less than 0.1% measured at room temperature and at 10 kHz. Dielectric tunabilities of, 3, 15, and 70% were measured on x =0.2, 0.25 and 0.3 under 20 kV/cm bias field at 10 kHz and at room temperature.

Local symmetry breaking in PbxSr1−xTiO3 ceramics and composites studied by Raman spectroscopy

Local symmetry breaking in PbxSr1−xTiO3 (PST) solid solutions was revealed by Raman spectroscopy below and above the ferroelectric phase-transition temperature. In the paraelectric phase, local symmetry breaking associated with the polar clusters localized mostly at grain boundaries in ceramic samples leads to the activation of the polar modes far above the dielectric maximum. This effect was found remarkably enhanced in the PST:MgO composites due to the compositional inhomogeneity of the grain boundaries and the intergrain stresses in the composite. In the ferroelectric phase, the degeneracy of the E(TO1) soft mode was lifted due to translational symmetry breaking in the solid solutions with x=0.2 and 0.3, where the substitution of Sr by Pb replaces partially the ionic bonding between the A cations and the oxygens by a stronger covalent bonding.

Study of Dielectric Properties of (Sr1-xPbx)TiO3: MgO Composites for Field Tunable Devices

(Sr1-xPbx)TiO3 (SPT) ceramics have low loss tangents and high dielectric tunabilities under DC bias fields at room temperature, but they have the disadvantage of high dielectric constants. In order to exploit these materials for microwave applications, the reduction of dielectric permittivities is necessary. Thus, the composites of the SPT system by the addition of a non-ferroelectric oxide such as MgO were prepared and electrical properties were measured. Loss tangents of the composite sintered at the same temperature as SPTs sintering were less than 0.3% in paraelectric region just above the transition temperature and the dielectric tunabilities of ~20% at 20 kV/cm and ~35% at 40 kV/cm were observed at 10 kHz.

Frequency and field dependence dielectric properties of novel composites fabricated from (Sr1−xPbx)TiO3: Al2O3 component phases

Abstract Composites fabricated from (Sr 1− x Pb x )TiO 3 (SPT) and Al 2 O 3 are developed that show relative permittivity ∼100, tangent δ less than 0.005, and temperature coefficient of relative permittivity ∼700 ppm at a low frequency, 10 kHz over the range ∼150–40 °C. A dielectric tunability of ∼5% at 20 kV/cm field is maintained over the whole temperature range. X-ray diffraction reveals that after the fabrication, the second phase is not Al 2 O 3 but a composite of alternative phases in conjunction with SPT, which presumably contributes the tunability.

Dielectric response near the permittivity maximum in (Sr0.8Pb0.2)TiO3 ceramic solid solution

It is well known that the weak-field relative dielectric permittivity maximum ϵw(max) achieved at the paraelectric-ferroelectric phase transition in ceramic ferroelectric solid solutions in the perovskite structure family is a strong function of the processing conditions used in fabrications. Heretofore, the height and sharpness of the dielectric peak have often been regarded as good qualitative indicators of the quality and homogeneity of the solid solutions. In the SrTiO3–PbTiO3 solid solution system at low PbTiO3 concentrations, this sensitivity is again strongly evident. Now, however, even for samples with a very sharp ϵw(max) giving values >45000 at weak-field dielectric maximum temperature Tmax above the peak temperature, 1∕ϵw (ϵw: weak-field relative dielectric permittivity) departs from Curie-Weiss behavior more than 15°C above the Curie-Weiss temperature θ which now occurs above Tmax. The unusual condition Tmax

Dielectric properties of (Sr1-xPbx)TiO3, SPT ceramics (x = 0.05, 0.1, and 0.15) and phase transition of SPT (x = 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3)

Dielectric properties of (Sr1 - xPbx)TiO3-SPT (x = 0.05, 0.10 and 0.15) and phase transitions of SPT (x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) ceramic samples are investigated. At 10 kHz relative permittivity of SPT(x = 0.05) has one maximum, SPT(x = 0.10) and SPT(x = 0.15) show the main relative permittivity peaks and the secondary peaks at lower temperatures. The primary dielectric constant peaks could be due to the phase transitions from the paraelectric to ferroelectric phases on cooling and the source of the secondary peaks is not clear. Lattice parameter vs. composition, x shows a linear relation and phase transition has also a linear relation to the composition.

DIELECTRIC PROPERTIES OF (Sr0.8Pb0.2)TiO3-MgO COMPOSITES AT LOW AND MICROWAVE FREQUENCIES

ABSTRACT (Sr0.8Pb0.2)TiO3-MgO (50:50 by weight) composites are fabricated and their dielectric properties are investigated at room temperature in the frequency range between 10 kHz and 26 GHz. Relative dielectric constant is ∼116. tan δ at 10 kHz is 0.0005 or less than 0.0005, but tan δ at higher frequencies increases to 0.006 at 4 GHz and 0.04 between 18 GHz and 26 GHz. The resonant methods show constant Q × f (Q: 1/tan δ, f: Frequency) ∼700 GHz in the frequency range of 2.5 GHz to 7 GHz, but the waveguide technique shows different values because of low accuracy in measuring tan δ.

(Sr1-xPbx)TiO3-MgO Composites for Field Tunable Applications

(Sr1-xPbx)TiO3 (SPT)-MgO composites are promising for room temperature electric field tunable applications. The composites show a significant processing dependence of dielectric properties. This paper reviews dielectric characteristics of SPT-MgO composites, such as permittivity, loss tangents, dielectric maximum temperature, tunability, and hysteresis under bias. In addition, factors which influence tunability and dielectric properties are described.

Dielectric Mixing as Evidenced in a Wide Range of (Sr0.8Pb0.2)TiO3-MgO Composites

Using a composite of a high dielectric permittivity (ϵ) ferroelectric and low ϵ oxide to check dielectric mixing rules, often the high ϵ ferroelectric is strongly sensitive to elastic and dielectric boundary conditions. So its ϵ changes as volume fraction and microstructure change invalidating any checking. In the strontium lead titanate (SPT)-magnesium oxide composites reported here, the SPT is well above its Curie point and much less sensitive, however, both phases contain pores. Since the pore fractions are low and almost constant, the system may be treated as quasi-two-phase and is found to follow closely the model proposed by Wakino.

Effect of Cold Pressing on Dielectric Properties of (Sr0.8Pb0.2)TiO3-MgO Composites

(Sr0.8Pb0.2)TiO3-MgO (50:50 by weight) composites are prepared and their dielectric properties are investigated. The dielectric properties of the samples prepared by using the green samples prepared under different cold pressing conditions are compared. The cylindrical samples prepared by using uniaxial pressing (UP) followed by cold isostatic pressing (CIP) show the higher quality of dielectric properties than the plate samples prepared by using only UP. It is found that the forming pressure before CIP also influences the dielectric constant of the sintered products. Furthermore, the dielectric constant of the rectangular composite samples cut out of the disk samples is direction dependent with respect to the UP direction while the tan δ of the composites is almost independent of the measurement directions. Communicated by Dr. George W. Taylor