La-modified Pb Research Articles

Electric field-induced irreversible phase transformations in Pb(Zr, Ti)O3-based piezoceramics

La-modified Pb(Zr,Ti)O3 (PLZT) (d33 ∼ 650 pC/N) and unmodified Pb(Zr1-x, Tix)O3 in the composition range (0.35 = x ≤ 0.51) were electrically poled through a novel powder poling technique. The mechanisms of large piezoelectric response in morphotropic phase boundary (MPB) and non-MPB-based compositions were discussed. Structural analysis suggests MPB-based compositions undergo irreversible structural phase transformation and lattice distortion after poling, and non-MPB undergo irreversible structural phase transformation. In the framework of theories, it has been argued that the MPB compositions satisfy the polarization rotation cum structural distortion phenomenon and non-MPB-based compositions follow the polarization rotation model.

Ferroelectric-relaxor boundary in La-modified Pb(Mg1/3Nb2/3)O3-xPbTiO3 crossover showing enhanced dielectric and piezoelectric properties

The dielectric and piezoelectric properties of La-modified Pb(Mg1/3Nb2/3)O3-xPbTiO3 crossover ceramics were systematically studied. In this crossover region, there is a ferroelectric-relaxor boundary separating the ferroelectric and relaxor states, which is determined by the spontaneous transition from relaxor to ferroelectric state with decreasing temperature. At the ferroelectric-relaxor boundary, the maximum permittivity increases from 18,200 to 23,500, and piezoelectric coefficient (d33) increases from 300 pC/N to 450 pC/N accompanied by the electrostrain improved from 0.09% to 0.12%, as compared with adjacent ferroelectric specimen. These enhancements may originate from the low energy barrier for polarization rotation induced by the existence of spontaneous transition and the coexistence of macrodomain and polar nanodomain configuration. This work indicates that the ferroelectric-relaxor boundary in crossover region may become an effective approach to enhance the dielectric and piezoelectric properties of ferroelectric materials.

La-modified Pb(Lu1/2Nb1/2)O3 antiferroelectric ceramics with high energy storage density

LaxPb1−3x/2(Lu1/2Nb1/2)O3 antiferroelectric (AFE) ceramics with compositions of x=0, 0.01, 0.02, 0.03, 0.04, 0.05 were successfully prepared and characterized by means of X-ray diffraction (XRD), AFE and dielectric measurements. The effects of La3+ content on the properties of the ceramics are discussed. The maximal value of the dielectric constant (ɛ′) and the Curie temperature (Tc) both gradually decrease from 662 to 356 and 272°C to 240°C respectively with increasing La3+ content from 0 to 0.05. The electric field at which the material transitions from the AFE phase to ferroelectric (FE) phase increases along with increasing La3+ content and the maximum value of energy storage density is estimated to be 3.85J/cm3 at 200°C based on the unsaturated double hysteresis loops. These results indicate that La-doping is an effective method to improve the energy storage density of the Pb(Lu1/2Nb1/2)O3 AFE ceramics.

Ultrafast crystallization kinetics in (Pb,La)(Zr0.30Ti0.70)O3 thin films by pulsed excimer laser annealing

The crystallization kinetics of laser-annealed Lamodified Pb(Zr,Ti)O₃ (PLZT) thin films on LaNiO₃-coated silicon substrates were investigated for substrate temperatures below 400 °C. A KrF excimer laser having a ~20 ns pulse width and an energy density ~40 mJ/cm² was used to crystallize the films. The perovskite phase developed with cumulative laser pulse exposures; it was found that ~380 to 400 nm thick films could be fully crystallized for a total exposure time of 0.1 to 1 ms. Laser-crystallized films exhibited comparable dielectric and ferroelectric properties to those prepared by rapid thermal annealing at 650 °C for 1 min. The evolution of the dielectric properties as a function of the number of laser strikes suggests that once nuclei are present, they rapidly grow through the depth of the film. This is consistent with the electron microscopy results, which did not show a well-defined planar growth front that proceeds from the top to the bottom of the film. The resulting films showed comparatively large lateral grain sizes (on the order of 250 to 300 nm), with high defect concentrations. The nucleation and growth mechanisms were modeled using Avrami kinetics under rate-dependent and nonisothermal conditions. These results indicate that PLZT crystallization via laser annealing is nucleation-limited.

Relaxor Dielectric Behavior in Lanthanum-Modified Pb(Fe1/2Nb1/2)O3 Ceramics

Pure perovskite phase of La-modified Pb(Fe 1/2 Nb 1/2 )O 3 (PLaFN) ceramics was prepared by the conventional solid-state reaction method through the wolframite precursor route with the lanthanum concentration up to 20 mol%. Due to the substitution of La 3 + for Pb 2 + ions at the A-site of the perovskite structure, the PLaFN ceramics exhibit apparent relaxor dielectric behavior. The temperature of the ferroelectric-paraelectric phase transition decreases greatly with the addition of lanthanum and fluctuates slightly with the increase of lanthanum content. An especially broad dielectric shoulder appears in the paraelectric phase of the PLaFN ceramics and the temperature of the onset of dielectric shoulder also fluctuates with the lanthanum concentration, where the dielectric constant exhibits less dependency on temperature and frequency around a large temperature range. The obtained PLaFN ceramics show low dielectric loss, considered correlating with the complex La-substituted defects and mainly A-site lead vacancies. Which decreases the reduction of Fe 3+ to Fe 2+ ions and pins down the rotation of space-charge polarization, leading to the decrease of dielectric loss of the iron-containing compound.

Electro-Optic and Magneto-Optic Photonic Bandgap Materials Kevin

ABSTRACTThis work presents a study of electro-optic and magneto-optic films made by a Metal-Organic Chemical Liquid Deposition (MOCLD) method. Electro-optic thin film, La-modified Pb(Mg1/3Nb2/3)O3-PbTiO3 (PLMNT) and magneto-optic thin film, rare earth doped yittrium iron garnet (YIG) have been grown at different conditions. Low temperature growth on buffered semiconductor substrates has been studied for semiconductor device integration. High quality PLMNT film with EO coefficient of 1x10-16 (m/V)2 was obtained with MOCLD. Doped and undoped YIG onto MgO and glass substrates and also onto buffered semiconductors were successfully deposited using MOCLD method. Several of these films had successful rotations that were of device quality. Based on these high quality functional films, two dimensional photonic bandgap waveguide structures were designed and simulated.

A triclinic phase of relaxor La-modified Pb(Zr0.65Ti0.35)O3 and its structure at 40 K by high-resolution neutron diffraction

The phase transitions and structure of 7% La-modified Pb(Zr0.65Ti0.35)O3 (PLZT 7/65/35) at 40 K were investigated using high-resolution powder diffraction. The high-resolution data suggest the existence of an alternate phase, which is not expected from the widely accepted phase diagram. By structural analysis and Rietveld refinement, the space group of this phase was determined to be F1 (the standard setting is P1 by adding face-centered generators), rather than the expected R3c or the reported Cm phase. The unit cell of this phase is deduced by doubling the primitive cubic cell along three main axes, cell parameters area a=8.14546(13) Å, b=8.18539(15) Å, c=8.16785(11) Å, and interaxial angles are α=90.1925(24)°, β=89.8785(26)°, and γ=90.1564(34)°. The tilting system of oxygen octahedra is āb̄c̄ instead of āāā in the R3c phase. The cation displacements and polarization are described in detail. The polarization direction was found to be along 〈112〉, not the main axes. The phase relationship and domain morphology are discussed in light of this triclinic phase, suggesting that this phase is important to understand the complex phase transitions and domain morphology in this series of materials. The experimental results suggest that this triclinic phase may extend to other compositions and temperature range.

Phase Diagram in La-modified Pb(Sc 1/2Nb 1/2)O 3–PbTiO 3 Binary Ceramics System

The phase boundaries in La-modified Pb(Sc1/2Nb1/2)O3–PbTiO3 system (La-PSN/PT), expressed as Pb(1-x)Lax[(Sc1/2Nb1/2)yTi(1-y)](1-x/4)O3, were determined. The phase diagram was found to consist of three phases: paraelectric cubic, ferroelectric tetragonal and ferroelectric rhombohedral at room temperature. The Curie temperature of the solid-solution ceramics decreases with increasing La content. The plot of the Curie temperatures of the samples with different La-PSN/PT compositions obtained at about 25°C, presents a curve from the composition of La-PSN/PT 2.5/100/0 to 25.5/0/100. Above room temperature, the morphotropic phase boundary (MPB) plots a straight line from composition 0/57.5/42.5 to 12.2/60.9/39.1. The electrical properties of the binary ceramics materials near the MPB were investigated.