PbTiO3 Concentration Research Articles

Phase Transitions in Modified Na1/2Ba1/2TiO3-SrTiO3-PbTiO3 Solid Solutions

The addition of NaNbO3 and PbMg1/3Nb2/3O3 to 0.4Na1/2Bi1/2TiO3-0.4SrTiO3-0.2PbTiO3 causes transfer from ferroelectric state to relaxor. The opposite was observed when concentration of PbTiO3 is increased in (1-x-y)Na1/2Bi1/2TiO3-xSrTiO3-yPbTiO3. The studied solid solutions represent the case of very complex mixing of different ions in the same positions of crystallographic lattice. The weakening of ferroelectric properties is considered to be an important reason developing of relaxor state.

PHASE TRANSITIONS IN Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 SOLID SOLUTIONS

ABSTRACT Studies of nature of polarization in ternary solid solutions of Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 were done, using measurements of dielectric properties and polarization hysteresis loops. Various stages of relaxor behavior depending on concentration of PbTiO3 were established and compared with other known ferroelectric relaxors.

Synthesis and characterization of pseudo-ternary Pb(Fe1/2Nb1/2)O3-PbZrO3-PbTiO3 ferroelectric ceramics via a B-site oxide mixing route

Perovskite phase formation and dielectric/ferroelectric properties of the pseudo-ternary Pb(Fe1/2Nb1/2)O3-PbZrO3-PbTiO3 (PFN-PZ-PT) ferroelectric ceramics have been investigated as promising materials for multi-layer ceramic capacitors. Complete solid solution with pure perovskite phase can be formed in this system in the whole composition range studied using conventional solid-state reaction method via a B-site oxide mixing route. Crystal lattice of the ceramics obtained shrinkages with the increase of the concentration of Pb(Fe1/2Nb1/2)O3 (PFN) and expands with the increase of the content of PbZrO3 (PZ). With the increase of the concentration of PbTiO3 (PT), crystal structure of PFN-PZ-PT changes from pseudo-cubic ferroelectric phase to tetragonal one while retains the fraction of PFN as constant. A morphotropic phase boundary (MPB) forms at the composition of 42 mol% PT regardless of whatever concentration of PFN, and the content of PFN affects little on the composition of MPB. The preliminary phase diagram of the PFN-PZ-PT system is determined by X-ray diffraction (XRD) measurements combining with dielectric/ferroelectric characterization. Dielectric measurements indicate that the value of dielectric maximum (ɛm) and the temperature where ɛm appears (Tm) increase with the increase of the concentration of PT. However, PFN exhibits opposite effects, i.e., ɛm increases with the increase of the concentration of PFN accompanied by the decrease of Tm.

Structural and Dielectric Studies of the Phase Transitions in Pb(Yb1/2Ta1/2)O3-PbTiO3 Ceramics

A dielectric phase diagram of the pseudobinary (1-x)Pb(Yb1/2Ta1/2)O3-xPbTiO3 solid solution system was determined. The crystal structures and the dielectric properties were investigated in terms of the PbTiO3 concentration. As the PbTiO3 concentration increases, the crystal structure changes from monoclinic to pseudocubic and then to tetragonal. A morphotropic phase boundary that separates the pseudocubic phase from the tetragonal phase has been determined at x ≈0.5. The phase transition of pure Pb(Yb1/2Ta1/2)O3 is unusual in that it undergoes a paraelectric-antiferroelectric transition at 310°C and another secondary antiferroelectric-ferroelectric transition at about 177°C. This successive phase transition characteristic confers a rather unique feature on the (1-x)Pb(Yb1/2Ta1/2)O3-xPbTiO3 phase diagram.

Structural Phase Transition in La-Substituted Pb[(Yb 1/2Nb 1/2) 0.88Ti 0.12]O 3 Relaxor System

We have investigated the effect of substitution of La2O3 + Yb2O3 to the perovskite solid solution near the composition (PbYb1/2Nb1/2O3)0.88–(PbTiO3)0.12 in the chemical formula (1-x)[(PbYb1/2Nb1/2O3)0.88 (PbTiO3)0.12]–xLaYbO3. When x = 0.0 and x =0.01, these solid solution have partially disordered pseudocubic structure and behave as a ferroelectric relaxor. For x ≥0.02, the character of phase transition changes from a ferroelectric relaxor type to an antiferroelectric one and the transition temperature surprisingly increases with LaYbO3 addition. In this composition range, the solid solution displays a sharp antiferroelectric transition. The effect on the tendency toward antiferroelecticity with increasing LaYbO3 content is displayed in restoring of the superlattice reflections due to antiferroelectric order. From the structural study of ceramic specimen having various PbTiO3 and LaYbO3 concentration, we have constructed a portion of phase diagram of pseudoternary PbYb1/2Nb1/2O3–PbTiO3–LaYbO3 system.

Observation of the Domain Motion in Ferroelectric Single Crystals with a Diffuse Phase Transition

Optical or electron microscopes have been usualy used to observe ferroelectric domains. But they have some difficulties in applying an external electric field or in changing the temperature of a sample. A CCD microscope has been developed for the domain observation by combining a low magnification object-lens and a high resolution CCD sensor. The CCD microscope revealed more than ×1000 magnification on a CRT display with a very bright view. Moreover, it is easy to apply an electric field on the sample because of a sufficient distance between the object-lens and the sample. The image of the domain motion is instantaneously recorded with a VTR. Single crystals of the (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 system prepared by the flux method were used. This solid solution system exhibits a morphotropic phase boundary between rhombohedral and tetragonal phase near x=0.1. The phase transition behavior from ferroelectric to paraelectric phase becomes sharp with increasing PbTiO3 concentration (x) in comparison with a diffused phase transition in Pb(Zn1/3Nb2/3)O3. Our observation demonstrated that the ferroelectric domain motion is closely correlated with the phase transition diffuseness and dielectric relaxation.

Preparation and properties of PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 composition

We prepared and characterized PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 stoichiometric composition. We examined microstructures, sintering behavior, and phase compositions in this system and prepared several new compositions, which have a single phase perovskite structure and a high dielectric constant (28000), by low sintering temperature (950–1020 °C). These compositions have a high electrical resistivity (1013 ohm-cm), which is about 1000 times higher than those of Pb(Fe½Nb½)O3 and Pb(Fe⅔W⅓)O3 based ceramics. The new compositions can be readily prepared into a single phase perovskite without a detectable amount of pyrochlore second phase by a simple method of mixing and calcining the constituent oxide and carbonate powders. Our dielectric measurements and XRD data establish the correlation between the decrease in dielectric constant and the presence of pyrochlore second phase. The effects of PbTiO3 dopant were quantitatively measured and our data showed that at a low (10 mole %) PbTiO3 concentration, the Curie temperature increases 6.6 °C for every mole % PbTiO3 dopant in the new compositions. The dielectric constant increases from 18000 in the undoped composition to 27 100 and 29000 by a PbTiO3 dopant concentration of 5% and 10%, respectively. The maximum dissipation factor also decreases from 0.10 in the undoped composition to 0.055 in the 10% PbTiO3 doped composition. The electrical resistivity, ρ, decreases with the PbTiO3 dopant concentration, t, following the ρ = ρ0 exp (–t/t0) relation where ρ0 ≍ (9.6 ± 0.2) × 1012 Ωcm and t0 ≃ 0.044.