Lanthanum Modified Lead Titanate Research Articles

Structural description of temperature evolution of polar clusters in PLZT relaxor ceramics

ABSTRACT This letter quantifies the phases by Rietveld refinement of perovskite relaxor ferroelectric ceramics of lanthanum-modified lead titanate zirconate (PLZT 9/65/35) as a function of temperature. The refinement results show the relative limit of phases between the polar electrical percolation and their vanishing as a function of temperature, coincident with dielectric measurements. The quantification of polar/nonpolar phases simultaneously is structural description of the polar clusters in relaxor ferroelectrics ceramics. The temperature changes in the polar/nonpolar phase ratio suggest a volume dynamism of the polar clusters as a function of temperature.

Enhanced electrocaloric analysis and energy-storage performance of lanthanum modified lead titanate ceramics for potential solid-state refrigeration applications

The unique properties and great variety of relaxer ferroelectrics make them highly attractive in energy-storage and solid-state refrigeration technologies. In this work, lanthanum modified lead titanate ceramics are prepared and studied. The giant electrocaloric effect in lanthanum modified lead titanate ceramics is revealed for the first time. Large refrigeration efficiency (27.4) and high adiabatic temperature change (1.67 K) are achieved by indirect analysis. Direct measurements of electrocaloric effect show that reversible adiabatic temperature change is also about 1.67 K, which exceeds many electrocaloric effect values in current direct measured electrocaloric studies. Both theoretical calculated and direct measured electrocaloric effects are in good agreements in high temperatures. Temperature and electric field related energy storage properties are also analyzed, maximum energy-storage density and energy-storage efficiency are about 0.31 J/cm3 and 91.2%, respectively.

A structural evidence of polar clusters in PLZT relaxor ceramics

ABSTRACTIn this paper, a quantification of the polar/non-polar phases of perovskite single-phase relaxor ferroelectric ceramics of lanthanum modified lead titanate zirconate (PLZT x/65/35, x = 5, 8, 9 and 10%) was performed by Rietveld refinement using measurements obtained with Cu kα radiation and with high-resolution synchrotron radiation. The refinements were performed concerning two crystalline phases, being one of them nonpolar (Pm-3m) and the other polar. The refinement results showed the relationship between the polar/nonpolar phases and the La content in PLZT, suggesting the existence of polar clusters of relaxor ferroelectric ceramics.

The relationship between ferroelectric domain pattern and properties of PLT21 ceramics

The light passing through a ferroelectric crystal tends to split into several separate beams due to refraction and reflection at the domain walls. This interaction of light with ferroelectric domains becomes one of the most important features of modern optoelectronic and nonlinear optics materials. Recently, lanthanum modified lead titanate, Pb(1-x)LaxTiO3, (PLT) has become popular because it possesses interesting properties such as a lower Curie temperature, a lower coercive field, and smaller remanent polarizations than PZT and has great potential for nonlinear optical and electro optical applications. In this work, we propose a simple model taking into account the optical transmission and rearrangement of the ferroelectrics domains structure on the PLT21 ceramic in temperature function. The variation of dielectrical and optical measurements in function of temperature were observed and correlated with the optical visualization of ferroelectric domains.

Domain structure and polarization reversal in ferroelectric lanthanum-modified lead titanate ceramics investigated by piezoresponse force microscopy

In this work, the ferroelectric domain structure of (Pb0.79La0.21)TiO3 transparent ceramics and its response to an applied electric field were investigated by piezoresponse force microscopy (PFM). A qualitative three-dimensional reconstruction of the domains by PFM measurements revealed that the domain structure consists in stripes in two size scales (micro and nanometer) separated by 90° domain walls coexisting with 180° domains. While the nanoscale 90° domains were found arranged in organized structures, (e.g., lamellas, herringbones, and other unusual configurations), the 180° domains form a “labyrinth” structure, typical of ferroelectrics with a degree of disorder. Local application of an electric field reveals different coercive voltages to reorient 180° and the two types of 90° domains and the appearance of a different nanoscale 90° domain structure after poling. While the labyrinth structure is destroyed with relative low voltages, the created 90° domains structure persists, avoiding the formation of a single-domain structure.

The dielectric anomaly and pyroelectric properties of sol–gel derived (Pb,Cd,La)TiO3 ceramics

Cadmium and lanthanum modified lead titanate ceramics with chemical formula (Pb0.85Cd0.05La0.10)Ti0.975O3 were prepared by a sol–gel process. The diffuse dielectric anomaly found in the temperature dependence of dielectric permittivity is a competitive effect of dielectric polarization and electrical conduction caused by the oxygen vacancies, which are extrinsically formed during the sample preparation process. The impedance analysis indicates that the resistance of the sample decreases with the increasing in temperature indicating a negative temperature coefficient of resistance behavior, which is caused by the La3+ substitution in Pb2+. The Arrhenius analyses, which are performed on the permittivity data above ferroelectric–paraelectric phase transition temperature and the imaginary part of the impedance, respectively, imply that two different polarization mechanisms are involved in the temperature range of 25–600 °C. Besides, the ferroelectric and pyroelectric properties of PCdLT ceramic are also investigated. The high pyroelectric coefficient (338.8 μC/m2K) and figure of merits (16.84 × 10−6 Pa−0.5) make this material a potential candidate for pyroelectric detectors.

Effect of manganese on thermal, structural and magnetic properties of lanthanum modified lead titanate nanoceramics

PbTiO3 (PT) and La/Mn modified PbTiO3 (PLMT) nanoceramics were prepared by mechanical alloying and thermal methods. A thermal analysis technique has provided some important clues and guidelines for formation of required compounds and their thermal stability. The formation of single-phase perovskite compounds was confirmed by an X-ray diffraction technique. The field emission scanning electron micrograph of the compounds shows that materials have well-defined granular morphology. La/Mn substitution at Pb/Ti sites reduces the lattice distortion, and decreases ferroelectric phase temperature of lead titanate. Room temperature P–E loop confirms the existence of ferroelectric ordering in the sample. The nonlinear M–H hysteresis loop with small magnetization revealed that a ferromagnetic property is observed in PbTiO3 due to the substitution of Mn at Ti-sites of PbTiO3

Members of Lanthanide Family as Dopants in Relaxor PLZT Ceramics

Nowadays, the research and industrial interests about the luminescent properties of lanthanide family doped PLZT (lanthanum modified lead titanate zirconate) ceramics are increasing. Nevertheless, the improvement of other properties in these lanthanide doped systems, such as electro-optic and dielectric, were not much explored. This paper briefly discusses dielectric properties, the relaxor like behavior, and the extent of the ferroelectric/relaxor phases as a function of the lanthanide dopant. The enhanced relaxor properties were found for some compositions, and the lanthanide family doping process is proposed as an effective approach to increase the temperature stability of the relaxor-like phases.

Pressure-temperature-La concentration three-dimensional phase diagram of La-modified PbTiO3 determined by Raman scattering

A detailed Raman scattering study was performed on lanthanum-modified lead titanate (PLT) with compositions varying from pure PbTiO3 to La 20.0 at. %, for temperatures ranging from 8 K to temperatures above the Curie temperature and hydrostatic pressures up to 7.5 GPa. A complete La concentration-pressure-temperature three dimensional phase diagram was determined, by using the E(TO1) soft mode frequency as the main probe.

기계화학공정에 의한 (Pb, La)TiO3나노 분말의 합성 및 소결 특성 연구

In this study, we successfully synthesized a nano-sized lanthanum-modified lead-titanate (PLT) powder with a perovskite structure using a high-energy mechanochemical process (MCP). In addition, the sintering behavior of synthesized PLT nanopowder was investigated and the sintering temperature that can make the full dense PLT specimen decreased to below <TEX>$1050^{\circ}C$</TEX> by using <TEX>$Bi_2O_3$</TEX> powder as sintering agent. The pure PLT phase of perovskite structure was formed after MCP was conducted for 4 h and the average size of the particles was approximately 20 nm. After sintered at 1050 and <TEX>$1150^{\circ}C$</TEX>, the relative density of PLT was about 93.84 and 95.78%, respectively. The density of PLT increased with adding <TEX>$Bi_2O_3$</TEX> and the specimen with the relative densitiy over 96% were fabricated below <TEX>$1050^{\circ}C$</TEX> when 2 wt% of <TEX>$Bi_2O_3$</TEX> was added.

Room Temperature Preparation of Nano-Sized Lanthanum Modified Lead Titanate Powder with Perovskite Structure via Mechano-Chemical Technique

Room Temperature Preparation of Nano-Sized Lanthanum Modified Lead Titanate Powder with Perovskite Structure via Mechano-Chemical Technique

Influence of electrode configuration on dielectric properties of ferroelectric films with interdigital and parallel plate electrodes

The interdigital electrodes (IDEs) and parallel plate electrodes (PPEs) were prepared by photolithographic techniques and dc sputtering on rf magnetron sputtered lanthanum-modified lead titanate (PLT) films, respectively. The PLT films with IDEs and PPEs exhibit almost the same permittivity at 1kHz, while the dielectric constant and loss of PLT films with IDE decrease faster than those of the films with PPE as increasing the frequency. The permittivity of the films with IDE can be calculated using a previously developed analytical model. The reasons for the impact of the IDE and PPE on dielectric properties of the films were discussed.

Direct characterization of nanoscale domain switching and local piezoelectric loops of (Pb,La)TiO3 thin films by piezoresponse force microscopy

〈111〉 and 〈001〉, 〈100〉 preferentially oriented lanthanum-modified lead titanate thin films have been studied at the nanometre scale by means of piezoresponse force microscopy. The nanoscale domain structures, domain switching, and local piezoelectric loops of the films have been analysed. The imaging of the domain structures after the application of a dc field suggests the existence of 90° and 180° domains within the regions with intermediate contrast. The variation of piezoresponse under an electric field in domains of two types has been discussed. Significant differences have been found between the local piezoelectric loops measured in the films deposited on different substrates. These differences are related to the different textures present in the films.

Enhancement of the 90° domain-wall mobility in sol-gel (Pb,La)TiO3 thin films prepared by multiple deposition and crystallization

Sol-gel lanthanum-modified lead titanate thin films deposited onto Si-based substrates with two different processing conditions have been studied. The films have been processed with a single crystallization or with a multiple deposition and crystallization process. A preferential ⟨001⟩,⟨100⟩-mixed orientation is present in the two types of films. The dependence of the dielectric permittivity on frequency and field amplitude at subswitching fields, permittivity versus temperature curves, and ferroelectric hysteresis loops have been measured in the films. Both types of films present Rayleigh-type behavior with no differences between them, which suggests a similar density of defects in both films. Higher values of remanent polarization and dielectric permittivity, when approaching the transition temperature, have been achieved for the film prepared with the multiple deposition and crystallization process when compared with the obtained ones in the film prepared with a single crystallization. This is due to a lower clamping effect and an enhancement of the 90° domain-wall mobility in the former, as a consequence of the lower residual stress present in this film, achieved by means of the multiple deposition and crystallization process.

923 誘電率変化を用いた指向性可変ミリ波アンテナの創製(GS-16 センシング,研究発表講演)

This paper presents a directivity reconfigurable antenna for millimeter-wave communication. Reconfiguration is carried out by changing the dielectric constant of ferroelectric film. The ferroelectric film is composed of lanthanum modified lead titanate (PLT) and deposited on micro strip line by RF sputtering. The dielectric constant of PLT has temperature dependence, so by using heater elements we can change the dielectric constant of PLT film. Heater elements are laid out beside micro strip line. By switching heater element the dielectric constant is periodically changed, and the characteristic of antenna will be reconfigured. As a first step, we analyzed two kind of antenna device by using FDTD(Finite Difference Time Domain) method, and fabricated them. And we developed a new numerical analysis program using CIP(Cubic Interpolated Peudo-Particle Scheme) method.

Indentation induced testing studies on lanthanum modified lead titanate ceramics

Results of indentation induced Vicker’s microhardness, internal stress, and fracture toughness studies in the load range of 0.1–10 N on lanthanum modified lead titanate (PT) ceramics bearing composition Pb1−xLaxTi0.96Fe0.02Mo0.02O3, where x=0.02, 0.05, 0.10, 0.15, and 0.20 are presented. The load dependence of Vicker’s hardness number (VHN) is explained on the basis of Hays and Kendall’s law. Load independent value of VHN is worked out by the application of Hays and Kendall’s law for different compositions of lanthanum modified ceramics and the same is shown to increase with the increase in lanthanum substitution. Internal stress, fracture toughness, and brittleness index for these samples have also been calculated using microindentation technique.

Electrical and optical properties of sol–gel derived La modified PbTiO3 thin films

Lanthanum modified lead titanate (Pb1−xLaxTi1−x/4O3) PLTx (x=0.08 i.e. PLT8) sol–gel derived thin films have been prepared on indium tin oxide (ITO) coated glass and quartz substrates using lead acetate trihydrate, lanthanum acetate hydrate and titanium isopropoxide as precursors along with 2-methoxyethanol as solvent and acetic acid as catalyst by spin coating method. The microstructure and surface morphology of the films annealed at 650°C have been studied by X-ray diffraction technique and atomic force microscope (AFM). XRD has shown a single phase with tetragonal structure and AFM images have confirmed a smooth and crack-free surface with low surface roughness. The dependence of leakage current on applied voltage show ohmic behavior at low field region with a space charge conduction mechanism at high fields. The wavelength dispersion curve of thin films obtained from the transmission spectrum of thin films show that the films have high optical transparency in the visible region.

High frequency dielectric relaxation in lanthanum modified PbTiO3 ferroelectric ceramics

Dielectric measurements of lanthanum modified lead titanate ceramics were carried out in a frequency and temperature range of 70 ´ 106Hz - 2 ´ 109Hz and 300 K - 420 K, respectively. Dielectric relaxation appears around 7 ´ 108Hz at room temperature, and the maximum of the dielectric relaxation was around 393 K, the transition temperature (Tc). The relaxation frequency passes through a minimum at Tc and the dielectric relaxation exists in both paraelectric and ferroelectric phases. A fitting of the experimental data with the Debye relations gives some keys for understanding the dielectric behavior of such materials.

Indentation induced testing studies on lanthanum modified lead titanate ceramics

Results of indentation induced Vicker’s microhardness, internal stress, and fracture toughness studies in the load range of 0.1–10 N on lanthanum modified lead titanate (PT) ceramics bearing composition Pb 1− x La x Ti 0.96Fe 0.02Mo 0.02O 3, where x=0.02, 0.05, 0.10, 0.15, and 0.20 are presented. The load dependence of Vicker’s hardness number (VHN) is explained on the basis of Hays and Kendall’s law. Load independent value of VHN is worked out by the application of Hays and Kendall’s law for different compositions of lanthanum modified ceramics and the same is shown to increase with the increase in lanthanum substitution. Internal stress, fracture toughness, and brittleness index for these samples have also been calculated using microindentation technique.

Influence of Precursor Solutions on the Ferroelectric Properties of Sol-Gel-Derived Lanthanum-Modified Lead Titanate (PLT) Thin Films

Precursor chemistry was found to have a dominant effect on the electrical properties of sol-gel-derived Pb0.85La0.15TiO3 (PLT15) thin films prepared using different precursor sources for lanthanum, namely, lanthanum acetate dissolved in acetic acid (LAA) and lanthanum 2-methoxyethoxide in 2-methoxyethanol (LMM). The LMM-derived PLT15 films had lower dielectric constants (KLMM= 394, KLAA= 548, measured at 100 kHz, applying 500 mV oscillation voltage), poorer polarization hysteresis characteristics, and higher leakage current densities (JLMM∼ 1.5 × 10−7 A/cm2, JLAA∼ 2 × 10−9 A/cm2, measured at 10 kV/cm field). Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) measurements in conjunction with Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicate that better removal of C–O moieties are the key step to yield improved electrical properties in these films. Possibly, C–O moieties reduce the metallic oxides to their corresponding metals and the presence of the metallic constituent(s) (e.g., lead), in turn deteriorate the electrical properties. In line with these postulations it was found that, when the pyrolysis temperature is increased from 450° to 550°C, the organic contents of LMM-derived films are reduced and their electrical properties are indeed comparable to that of the LAA-derived films.