Structural and electrical properties of Nd ion modified lead zirconate titanate nanopowders and ceramics

A modified sol-gel method is used for synthesizing Nd ion doped lead zirconate titanate nanopowders Pb_{1 - 3x}/2Nd_xZr₀.52Ti₀.48O₃ (PNZT) in an ethylene glycol system with zirconium nitrate as zirconium source. The results show that it is critical to add lead acetate after the reaction of zirconium nitrate with tetrabutyl titanate in the ethylene glycol system for preparing PNZT with an exact fraction of titanium content. It has been observed that the dopant of excess Nd ions can effectively improve the sintered densification and activity of the PNZT ceramics. Piezoelectric, dielectric and ferroelectric properties of the PNZT ceramics are remarkably enhanced as compared with those of monolithic lead zirconate titanate (PZT). Especially, the supreme values of piezoelectric constant (d₃₃) and dielectric constant (\it ε) for the PNZT are both about two times that of the monolithic PZT and moreover, the remnant polarization (P_r) also increases by 30%. According to the analysis of the structures and properties, we attribute the improvement in electrical properties to the lead vacancies caused by the doping of Nd ions.     

Structural and electrical properties of lanthanum-substituted lead titanate ceramics

The effect of lanthanum substitution on the structural, dielectric and piezoelectric properties of lead calcium titanate (PCT) ceramics is studied. Samples with compositional formula Pb_{0.76? x} La _x Ca_0.24Ti_0.98Mn_0.02O₃ (PLCT) (x?=?0–0.08, in steps of 0.02) were prepared by the conventional dry ceramic technique. Phase and structural analysis was carried out using XRD and SEM respectively. X-ray analysis confirmed the formation of single-phase compound with tetragonal crystal structure. Dielectric properties were studied in detail as a function of frequency and temperature. The Curie temperature (T _C) and tetragonality (c/a) was found to decrease with increase in lanthanum content. The Curie temperature was also confirmed from the thermal-expansion behaviour of the sintered samples. Piezoelectric coefficients (d ₃₃, d ₃₁, g ₃₃, g ₃₁, g _h, d _h, k _t and k _p) were measured at room temperature. From this study it is found that La³⁺ substitution helps in the improvement of electro-mechanical anisotropy.     

Structural and impedance spectroscopic studies of samarium modified lead zirconate titanate ceramics

The polycrystalline samples of Pb_1−xSm_x(Zr_0.60Ti_0.40)_1−x/4O₃ (PSZT) where x=0.00, 0.03, 0.06 and 0.09 were prepared by a high-temperature solid-state reaction technique. The preliminary structural analysis using X-ray diffraction (XRD) data collected at room temperature has confirmed the formation of single-phase compounds in tetragonal crystal system. The morphological study of each sample using scanning electron microscope (SEM) has revealed that the grains are uniformly distributed through out the surfaces of the samples. Using complex impedance spectroscopy (CIS) technique, the electrical impedance and modulus properties of the materials were studied in a wide range of temperatures at different frequencies. The impedance analysis indicates the presence of bulk resistive contributions in the materials which is found to decrease on increasing temperature. The nature of variation of resistances with temperature suggests a typical negative temperature coefficient of resistance (NTCR) type behavior of the materials. The complex modulus plots clearly exhibits the presence of grain boundaries along with the bulk contributions in the PSZT materials. The presence of non-Debye type of relaxation has been confirmed by the complex impedance analysis. The variation of dc conductivity (bulk) with temperature demonstrates that the compounds exhibit Arrhenius type of electrical conductivity.     

Thermally stimulated processes in samarium-modified lead titanate ferroelectric ceramics

The thermally stimulated processes in a samarium-modified lead titanate ferroelectric system are analyzed from the thermally stimulated depolarization discharge current. The discharge due to the space charge injected during the poling process, the pyroelectric response and a conduction process related to oxygen vacancies are evaluated considering a theoretical decomposition by using a numerical method. The pyroelectric response is separated from other components to evaluate the polarization behavior and some pyroelectric parameters. High remanent polarization, pyroelectric coefficient and merit figure values are obtained at room temperature.     

Effect of B-site isovalent doping on electrical and ferroelectric properties of lead free bismuth titanate ceramics

In the present work, zirconium modified bismuth titanate ceramics have been studied as potential lead-free ferroelectric materials over a broad temperature range (RT – 800 °C). Polycrystalline samples of Bi₄Ti_3−xZr_xO₁₂ (x=0.2, 0.4, 0.6) (BZrT) with high electrical resistivity were prepared using the solution combustion technique. The effect of Zr doping on the crystalline structure, ferroelectric properties and electrical conduction characteristics of BZrT ceramics were explored. Addition of zirconium to bismuth titanate enhances its dielectric constant and reduces the loss factor as it introduces orthorhombic distortion in bismuth titanate lattice which is exhibited by the growth along (0010) lattice plane. Activation energy due to relaxation is found to be greater than that due to conduction thus confirming that electrical conduction in these ceramics is not due to relaxation of dipoles. Remanent polarization of the doped samples increases as the Zirconium content increases.     

Electrical and thermal properties of lead titanate glass ceramics

Glass samples with composition of (50−X)PbO-(25+X)TiO₂-25B₂O₃ (where X=0, 5, 10 and 12.5 mol%) were prepared using conventional quenching technique. The glass transition temperature, T_g and crystallization temperature T_c were determined from the DTA. These glass samples were converted to glass ceramics by following two stage heat treatment schedule. The glass ceramic samples were characterized by XRD, SEM and dielectric constant measurements. The XRD results revealed the formation of ferroelectric lead titanate (PT) as a major crystalline phase in the glass ceramics. The density increases and the CTE decreases for all glass ceramics with increase in X (mol%). This may be attributed to increase in PT phase. The SEM results which show rounded crystallites of lead titanate, also supports other results. Hysteresis loops observed at room temperature confirms the ferroelectric nature of glass ceramics. The optimized glass ceramic sample exhibits high dielectric constant which is of technical importance.     

Polarization switching process of soft lead zirconate titanate bulk ceramics

The domain switching dynamics was investigated in Nb-doped Pb(Zr_0.52Ti_0.48)O₃ bulk ceramics through observing systematically the evolution of the hysteresis loops at frequencies ranging from 0.01 to 100 Hz and in a field of 7.5–35 kV/cm. The experimental results indicate that the hysteresis loops are remarkably dependent on the fields and the frequencies. The data are analyzed by the Merz equation. The analysis results reveal that the requirement to satisfy the Merz equation is saturated loops. Based on these results, we divided the polarization switching process into three regions.     

Characterization of lead zirconate titanate ceramics using surface acoustic wave

Lead zirconate titanate (PZT) is widely used as a piezoelectric transducer material for bulk and surface acoustic wave (SAW) devices. In this Paper a novel laser-ultrasound technique for measuring the SAW properties of PZT for quality control purposes is presented.     

Specific features of the electrical properties upon smeared phase transitions in multicomponent ferropiezoelectric ceramics based on lead zirconate titanate

The reverse dependences of the permittivity ? _r ^′ (E ₌) and the polarization and depolarization currents in multicomponent ferropiezoelectric ceramics based on lead zirconate titanate (PZT) are investigated over a wide range of temperatures. The results obtained make it possible to separate the effects associated with the phase transformation and the effects predominantly caused by the switching of the domain structure in the studied material. The assumption is made that two smeared phase transitions occur in the system under consideration.     

Comparison of piezoelectricity in Ta and La substituted lead calcium titanate ceramics

This paper reports the experimental investigations on the effect of La³⁺ and Ta⁵⁺ substitution on the structural characteristics and dielectric and piezoelectric properties of lead calcium titanate (PCT) ceramic. The PCT samples with A-site and B-site substitution having the composition formula Pb_0.76−x/2La_xCa_0.24(Ti_0.98Mn_0.02)_1−x/2O₃ and Pb_0.76Ca_0.24Mn_0.02Ti _0.98−5x/4Ta_xO₃, x=0 and 0.02, respectively_, were prepared using conventional solid-state reaction method. Phase formation and structural analysis were studied using X-ray diffraction and scanning electron microscopy, respectively. Dielectric constant (ε′) and loss tangent (tan δ) as a function of frequency were measured at room temperature as well as elevated temperature. Both ε′ and tan δ decreased with increase in frequency at room temperature. Curie temperature decreased with La and Ta doping in PCT ceramics due to a decrease in the tetragonality of PCT ceramics. Piezoelectric charge coefficients (d₃₃, d₃₁) increased with La³⁺ substitution due to reorientation of the grains and decreased with Ta⁵⁺ substitution because of the increase in porosity. Figure of merit d_hg_h increased and decreased with La and Ta substitution, respectively. A good ferroelectric behaviour is obtained for La substitution, while no hysteresis is obtained for Ta substitution.     

Development of perovskite and phase transition in lead cobalt niobate modified lead zirconate titanate system

Ferroelectric lead zirconate titanate–lead cobalt niobate ceramics with the formula (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃ where x = 0.0–0.5 were fabricated using a high temperature solid-state reaction method. The formation process, the structure and homogeneity of the obtained powders have been investigated by X-ray diffraction method as well as the simultaneous thermal analysis of both differential thermal analysis (DTA) and thermogravimetry analysis (TGA). It was observed that for the binary system (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃, the change in the calcination temperature is approximately linear with respect to the PCoN content in the range x = 0.0–0.5. In addition, X-ray diffraction indicated a phase transformation from a tetragonal to a pseudo-cubic phase when the fraction of PCoN was increased. The dielectric permittivity is remarkably increased by increasing PCoN concentration. The maximum value of remnant polarization P_r (25.3 μC/cm²) was obtained for the 0.5PZT–0.5PCoN ceramic.     

Anomalous dielectric behaviour of La(III) substituted lead titanate ceramics

In La(III) substituted PbTiO₃ ceramics the behaviour of the reciprocal dielectric constant in the paraelectric phase can be described by the relation $\text{1}\text{?～}\text{(T ? T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{\gamma }}$ with the exponent 1 ?γ<2 depending on the composition. This γ-value is an intermediate of values for Curie-Weiss behaviour (γ = 1) and of values connected with diffuse phase transitions (γ = 2) and increases with increasing La(III) concentration.An excellent agreement between experimental and calculated permittivity curves in the paraelectric phase can be achieved using an alternative equation consisting of a linear and a quadratic term with coefficients varying systematically with the composition. The last equation can be derived and interpreted by means of a physical model assuming the existence of heterophase fluctuations.     

Pressure-temperature phase diagrams for several modified lead zirconate ceramics

Using dielectric constant and loss measurements we have determined the pressure-temperature phase diagrams of four ferroelectric ceramics based on lead zirconate (PbZrO₃). The materials chosen for study all have pressure-induced ferroelectric to antiferroelectric transitions at ∼0.3 GPa. In all four materials, five phases were identified by comparing our results with studies, previously published by other workers, of the phase behavior of modified PbZrO₃ materials as a function of composition and temperature. The observed phases are the ideal cubic perovskite paraelectric phase, two rhombohedral ferroelectric phases, and two antiferroelectric phases, one orthorhombic and one pseudotetragonal. Comparison is made with previous temperature-composition studies of modified PbZrO₃ materials.     

Dynamic fatigue during polarization switching of lead zirconate titanate ceramics with variable ferroelectric hardness

The remanent polarization of lead zirconate titanate ceramics with variable ferroelectric hardness is experimentally studied in a strong ac field. The results obtained suggest that the main mechanism of multiplication of crystal defects that controls the fatigue rate of soft ferroelectric ceramics is the process of twinning and untwinning in crystallites during polarization switching. In hard ferroelectric ceramics, the formation of a hysteresis loop is accompanied by the formation of stable configurations of mechanical twins in crystallites due to secondary twinning. Polarization switching in these configurations does not induce twin-wall motion, and the fatigue rate is low.     

Electrical phenomena in barium titanate ceramics

We have studied the current voltage curves of BaTiO₃ ceramics, with fired silver electrodes, between 110–400°C. We have observed a current controlled negative resistance between low conductivity and high conductivity states. The passage from the low to the high conductivity state is accompanied by a brown coloration starting from the anode. Once the high conductivity state is reached it is impossible to return to the low conductivity state unless one anneals the sample for several hours at 400°C. We have measured the voltage distribution along the sample and the short circuited currents after applying a voltage. We interpret our results, assuming carriers injection, by means of the Rose and Lampert models of injection. In the low conductivity state the conduction is ohmic or due to electron injection, and in the high conductivity state there is a double injection regime. However the agreement of the results with the theoretical prediction is good only qualitatively. We think that a more elaborate model is necessary.     

Effects of alumina nano-particulates addition on mechanical and electrical properties of barium titanate ceramics

Ferroelectric BaTiO₃/xAl₂O₃ nanocomposite ceramics (when x = 0, 0.5, 1, 3 and 5 vol%) were fabricated from an in-house prepared BaTiO₃ powder and nano-sized Al₂O₃ powder by a solid state mixed-oxide method. Densities and grain sizes of the ceramics were found to gradually decrease with increasing content of Al₂O₃ addition. Mechanical properties such as Knoop hardness and Young’s modulus of BaTiO₃ were found to be improved with only 0.5 vol% of Al₂O₃ addition. Dielectric and piezoelectric properties of the nanocomposites with <1 vol% Al₂O₃ addition could be maintained and were comparable to the values of the monolithic BaTiO₃. Within the range of the BaTiO₃/Al₂O₃ nanocomposites investigated, this study suggested materials with acceptable electrical properties and better structural stability.     

Specific features of the thermal physical properties of relaxor ceramics based on lead zirconate titanate

The heat capacity and thermal expansion of ferroelectric relaxors based on lead zirconate titanate are studied near the diffuse phase transition. It is shown that no spontaneous phase transitions from the paraelectric phase to the ferroelectric phase and from the relaxor state to the normal ferroelectric state occur in an ensemble of nanometer-sized polar regions. It is noted that the transitions can be caused only by external electric fields or storage for a fairly long time.     

Electroluminescence in lead titanate single crystals

Electroluminescence in PbTiO₃ single crystals is studied with variation in applied electric field, frequency (20 Hz to 5 kHz) and temperature. The EL onset depends on the rate at which the dipole switches. Extremely sharp upward rising nature of the pulses of micro second duration suggest that there is a self maintained discharge in the dielectric due to secondaryγ _p mechanism. Frequency dependence of EL suggests that both the secondary mechanisms, viz. theγ _p andγ _i are active after the application of a high field and the critical field at which this occurs decreases with increase in the frequency of the applied voltage. Similarly the onset voltage decreases with increase in frequency. The temperature dependence of EL at the applied frequency of 50 Hz shows that the onset voltage is intimately connected with the coercive field of the crystal and it is minimum at the Curie point. The study suggests that EL occurs in the bulk and there is a breakdown in the dielectric due to an avalanche formation.