Structural and dielectric properties of phosphorous-doped PLZT ceramics

In the present work we have reported the unique effects of P₂O₅-doped PLZT ceramics with composition (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ +x wt% of P₂O₅ (wherex = 1, 3 and 5) prepared chemically by co-precipitation method. X-ray diffraction studies suggest that the prepared compound was very fine (10–25 nm), homogeneous and of rhombohedral symmetry. The apparent density of samples decreased with the P⁵⁺ additions. Studies of dielectric constant and dielectric loss as a function of frequency (10–1000 kHz) and temperature suggest that the compound undergoes diffuse type of phase transition without any sign of relaxor behaviour. With increasingx, dielectric constant was found to decrease appreciably, whereas Curie temperature (T_C) was found to increase     

Structural and dielectric properties of Bi modified PLZT ceramics

Polycrystalline samples of bismuth (Bi) doped lead lanthanum zirconate titanate (PLZT) with the general formula Pb_0.9(La_1−zBi_z)_0.1(Zr_0.65Ti_0.35)_0.975O₃, where [z=0.0, 0.3, 0.5, 0.7] near the morphotropic phase boundary (MPB) has been synthesized by a solid solution mixing technique. Some aspect of crystal structure of the compound at room temperature was studied using X-ray diffraction (XRD) technique. Detailed studies of dielectric constant (ε) and dielectric loss () obtained both as a function of frequency (100 Hz-100 kHz) at room temperature (RT) and temperature (RT-600 K) at 10 kHz suggest that compounds undergo ferroelectric-paraelectric phase transition of diffuse type. Both ac and dc conductivity have been studied over a wide range of temperature. The activation energy (E_a) of the samples was calculated from the plot of ac conductivity vs. inverse of absolute temperature. The temperature variation of resistivity shows that the compounds have negative temperature coefficient of resistance (NTCR).     

Thermophysical properties of PLZT ferroelectric ceramics with a nanopolar structure

The heat capacity, thermal expansion coefficient, and deformation of the PLZT-9/65/35 compound are studied in the temperature range 150–800 K. Diffuse anomalies are detected in the temperature dependences of the heat capacity and thermal expansion coefficient over wide temperature ranges of 250–650 and 330–550 K, respectively. The anomalous behavior of the heat capacity in the temperature range 250–650 K is shown to be caused by the appearance of two-level states (Schottky anomaly). The results obtained are discussed along with the data of structural and dielectric studies.     

Determination of local polarization properties of PLZT ceramics by PS-OCT

Femtosecond pump-probe laser technique has been applied for the diagnostics of a film adhesion to a substrate. A low frequency motion additional to acoustic vibrational modes of the film has been detected and related to film oscillation as a lumped mass element at a weak adhesion bond. The measurements of this low-frequency provide information on the strength of the interface. Long life time of the observed oscillation has remained unexplained.     

Temperature dependences of the dielectric properties of lithium-titanium ferrite ceramics

Temperature dependences of the real ?′ and imaginary ?″ parts of the complex permittivity of lithium-titanium ferrite ceramics are measured in the frequency range 10²?10⁶ Hz at different test-signal amplitudes and dc bias voltages. It is found that the dielectric characteristics of the ceramic samples drastically change in narrow temperature ranges. The assumption is made that relaxators whose reorientation is due to tunneling transitions of electrons inside “bivalent iron ion-trivalent metal ion” pairs are involved in polarization processes. Under certain conditions, the reorientation of relaxators can have collective character.     

Effect of trivalent iron substitution on structure and properties of PLZT ceramics

Polycrystalline samples of Fe-modified PLZT (lead lanthanum zirconate titanate) are prepared by a mixed-oxide reaction technique. The formation of the compound has been confirmed by X-ray powder diffraction studies. The unit cell structure of the material has been found to be rhombohedral. Fourier-transform infrared reflection (FTIR) spectra have been recorded to correspond the structural changes associated with the phase formation. The effects of Fe concentration on the microstructure and dielectric constant of PLZT materials have been investigated. The ferroelectric phase transition of PLFZT materials is studied using dielectric measurements, which shows a shift in the transition temperature towards the higher-temperature side with increased Fe ion concentration. The piezoelectric constants of this system are investigated by the same way of changed contents of Fe ion in the main PLZT compound. The optimum values of Q_m, k_p, and d₃₃ are 73, 0.32 and 406. The electrical conductivity increases with the increase in Fe ion concentration. PACS 77.80.Bh; 77.84.Dy; 77.22.Ch; 72.15.Eb; 06.60.Ei; 39.30.+w     

Dynamics of birefringence properties in 17/30/70 PLZT ceramics

Birefringent properties of PLZT ceramics (Pb₈₃La₁₇)(Zr₃₀Ti₇₀)O₃ were investigated by measuring the transverse electrooptic effect in a 0.2 mm-thick wafer at various speeds of external voltage changes. At least two types of internal polarized microregions of different physical nature in charge of the electrooptical properties are observed.     

Light-induced intrinsic defects in PLZT ceramics

This paper reports on an EPR study of a ferroelectric, 1.8/65/35, and an antiferroelectric, 2/95/5, of optically transparent Pb_1?y La_yZr_1?x Ti_xO₃ (PLZT) ceramics within a broad temperature range (20–300 K) after illumination at a wavelength of 365–725 nm. Illumination with ultraviolet light, whose photon energy corresponds to the band gap of these materials, at T<50 K creates a number of photoinduced centers: Ti³⁺, Pb⁺, and Pb³⁺. It is shown that these centers are generated near a lanthanum impurity, which substitutes for both the Pb²⁺ and, partially, Ti⁴⁺ ions through carrier trapping from the conduction or valence band into lattice sites. The temperature ranges of the stability of these centers are measured, and the position of their local energy levels in the band gap is determined. The most shallow center is Ti³⁺, with its energy level lying 47 meV below the conduction band bottom. The Pb³⁺ and Pb⁺ centers produce deeper local levels and remain stable in the 2/95/5 PLZT ceramics up to room temperature. The migration of localized carriers is studied for both ceramic compositions. It is demonstrated that, under exposure to increased temperature or red light, the electrons ionized into the conduction band from Ti³⁺ are retrapped by the deeper Pb⁺ centers, thus hampering the carrier drift in the band and the onset of photoconduction. The part played by localized charges in the electrooptic phenomena occurring in the PLZT ceramics is discussed.     

Technology of PLZT ceramics microfibers for multiferroics composites

Compactness and large energy conversion capacity are the main reasons of development of sophisticated ceramics materials in microfibers form, which are prepared for high-speed multiferroic systems and devices. These multifunctional composite applications are owing to coupling of electrical and magnetic properties, as well as additional thermal and mechanical properties. So that, they are suitable for magnetic sensors, electrically tunable non-linear transducers, and non-volatile memories. In our experiment, the thin fibers ceramics have been produced using special environmental chamber where the high temperature sintering can be protected by controlling such parameters as temperature and sintering atmosphere. Consequently, for these purposes structural and physical properties, preparation and thermal synthesis of micrometer sized lead lanthanum zirconate titanate (PLZT) fibers were investigated thoroughly. Since the phase transition properties of PLZT fibers differ much, the production process of fibers suffers from lack of proper high temperature control. Consequently, our experiments should help to eliminate this drawback, so that various technological conditions, parameters, and subsequent sintering atmosphere with different mixtures of PbO and ZrO were experimentally tested. Final conclusions include comparative analysis of obtained PLZT fibers ferroelectric phase transition properties to specific sintering atmosphere.     

Second-harmonic generation in “Cubic” PLZT ceramics

The temperature-dependent optical second-harmonic generation in thermally depoled La-doped lead zirconate titanate (PLZT) ceramics of composition 8/65/35 and 9/65/35 has been studied. A microscopic model for the anomalous phase transition behaviour of these compounds is suggested.     

ESR and optical spectroscopy of copper-doped PLZT electro-optic ceramics

2+ spectra in axial and cubic crystal fields. Cu²⁺ substitutes for Ti⁴⁺ and the excess charge can be compensated by La³⁺ on a nearest-neighbor site, thus creating axial symmetry. The centers of cubic symmetry are those where the charge is compensated in distant spheres. In contrast to pure PLZT, PLZT:Cu exhibits a new luminescence band peaking at 1.18 eV. This emission is ascribed to the ²T₂(D)→²E(D) transition of Cu²⁺(3d⁹) which can be excited either in the resonant 1.87 eV band or via charge-transfer excitation bands at 2.40, 2.57, and 3.03 eV. The absorption band at 1.45 eV is assumed to be that of Cu⁺ ions. Annealing in hydrogen and in oxygen atmospheres caused decrease and restoration, respectively, of the ESR and luminescence intensities as a consequence of Cu²⁺ conversion into Cu¹⁺ and vice versa. Received: 14 November 1997/Accepted: 8 December 1997     

Concentration dependences of the properties of multicomponent PZT-based piezoelectric ceramics in the morphotropic transition range

The following three ternary PZT-based systems are studied in detail: 0.98Pb(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃, 0.98(Pb_0.9727Sr_0.0273)(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃ + 1 wt% PbO, and 0.98(Pb_0.9727Sr_0.0273)(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃ + 2 wt % PbGeO₃, where 0.45 ≤ x ≤ 0.49 and the concentration step is Δx = 0.025. A number of concepts are formulated regarding the phase diagrams of PZT-type systems near the morphotropic transition. A scheme for real tetragonal-rhombohedral transformation is given. The maxima of the electrophysical characteristics of the solid solutions from the morphotropic range are shown to be caused mainly by an appearing intermediate phase. Analysis of the insulating, piezoelectric, and mechanical properties of the samples demonstrates that there is a group of solid solutions that are promising materials for high-temperature piezoelectric devices operating in the medium-frequency band.     

Infrared to visible frequency upconversion temperature sensor based on Er3+-doped PLZT transparent ceramics

Infrared to visible upconversion in erbium doped lead lanthanum zirconate titanate (PLZT) transparent ceramic is reported for the first time. Intense green upconversion emissions around 534 and 565 nm originating from the thermally coupled levels ²H_11/2 and ⁴S_3/2 are observed. The mechanism responsible for excitation of these emitting levels is sequential two photon absorption based on the temperature dependence of the emissions ratio, a high temperature (up to 610 °C) sensor is proposed, with various advantages over the existing glass-based sensors, such as higher thermal and mechanical resistances, better chemical stability and lower cost fabrication.     

Polarization switching in heterophase nanostructures: PLZT relaxor ceramics

The polarization switching is experimentally investigated in hot-pressed PLZT-x/65/35 ceramics with a lanthanum content from 5 to 12 at. %. The specific features in the temperature dependence of the polarization switching in a heterophase state are interpreted by analyzing the change in the switched charge measured over wide ranges of fields and temperatures. Particular emphasis is placed on the role of depolarization fields induced by interphase boundaries. A model of the evolution of polydomain nanostructures with a change in the temperature and in the response to an external field is considered. It is assumed that the low-temperature dielectric anomaly and the temperature hysteresis are associated with the loss of stability of a large-scale domain structure and its transformation into a nanodomain state.     

High temperature thermoelectric properties of Nb-doped ZnO ceramics

Solid-state reaction processing technique was used to prepare Zn_xNb_1−xO (0≤x≤0.02) polycrystalline bulk samples. In the present study, we find that their lattice parameters a and c tend to decrease with increasing amount of Nb additive. The electrical conductivity of all the Zn_1−xNb_xO samples increased with increasing temperature, indicating a semiconducting behavior in the measured temperature range. The addition of Nb₂O₅ to ZnO led to an increase in the electrical conductivity and a decrease in the absolute value of the Seebeck coefficient. The best performance at 1000 K has been observed for nominal 0.5 at% Nb-doped ZnO, with an electrical resistivity of about 73.13 (S cm⁻¹) and Seebeck coefficient of ∼257.36 μV K⁻¹, corresponding to a power factor (S²σ) of 4.84×10⁻⁴ Wm⁻¹ K⁻². The thermal conductivity, κ, of the oxide decreased as compared to pure ZnO. The figure of merit ZT values of ZnO-doped Nb₂O₅ samples are higher than the ZnO pure sample, demonstrating that the Nb₂O₅ addition is fairly effective for enhancing thermoelectric properties.     

In-situ Raman spectroscopic study of domain switching of PLZT ceramics

A specially designed apparatus was used to observe in-situ domain switching in lanthanum-doped lead zirconate titanate (PLZT) ceramics by Raman spectroscopy. Using the established technique, the variations in measured Raman spectrum of unpoled and appropriately poled PLZT ceramics under the application of dc voltage and during the process of electric fatigue were examined. It was confirmed that the intensity change in the soft mode of the Raman band is highly dependent on the orientation of the domain switching with respect to the polarization direction of Raman incident light. When the orientation of the specimen with respect to propagation directions (including polarization direction) of incident light and scattered light is appropriate, the Raman spectroscopy can allow a non-destructive and in-situ measurement of the domain switching in a microscopic scale. The relation between the domain switching and the measured Raman spectrum change is discussed for PLZT polycrystalline materials by developing criteria extended from a single-crystal model. PACS 81.70.Fy; 78.30.-j; 62.20.Mk     

Coupled temperature dependences of volume and compressibility

We present a new method for understanding the changes with temperature of the volume and compressibility of solids. These changes depend on five parameters: V ₀, B ₀, Θ, γ _G and δ _T. V ₀ and B ₀ are the atomic volume and bulk modulus at T?=?0?K, Θ is the Debye temperature, γ _G is the Grüneisen parameter, and δ _T is the Anderson–Grüneisen parameter. Equations for the temperature-dependent volume, bulk modulus and thermal expansion are given, and examples of the use of these equations are provided, with particular emphasis on the light actinides. For the elements, we examine the relationship between experimental values of γ _G and δ _T, and find no clear correlation. In particular, Swenson's rule, which states that the bulk modulus does not change with temperature if the volume is held constant, is a poor approximation to the data. We reveal a new useful approximate relationship between dB/dP and γ _G. We find that the thermodynamic quantity q, which describes the variation in γ _G with volume, distributes around 2, not around 1, as often assumed. We show that the thermal- expansion behavior of Si and Ge (including negative thermal expansion at low temperatures) are well described with the use of a two-level invar model.     

Pressure and temperature dependences of the elastic properties of rutile (TiO2)

Using ultrasonic techniques we have measured the pressure and temperature dependences of the six elastic constants of single-crystalline rutile (TiO₂). The pressure measurements were made in the range 0–20 kbar at room temperature, and the temperature measurements were made in the range 80–300°K at atmospheric pressure. Our results are in good agreement with the results recently reported by Manghnani et al., although our pressure derivatives are generally a few per cent smaller than theirs and our temperature derivatives a few per cent more negative (at 298°K). Nonlinear pressure dependences were observed for some of the elastic constants. A relation between the pressure-induced softening of two lattice modes (one optic and one acoustic) and a possible pressure-induced transition to the CaCl₂ structure is discussed. An approximate separation of the isobaric temperature derivatives of the elastic constants into “pure” volume and temperature contributions is considered. In particular, an attempt is made to estimate the magnitude of the error made in effecting this separation using equations applicable to cubic rather than tetragonal symmetry. It is shown that, in principle, these errors could be significant.