Ferroelectric phase transition in sol-gel derived Bi-doped PLZT ceramics

Polycrystalline samples of Bi-modified PLZT, [Pb_0.92(La_1–zBi_z)_0.08][Zr_0.60Ti_0.40]_0.98O₃ (abbreviated as PLBZT) for z = 0.0, 0.3, 0.6, 0.9 and 1 were prepared through a metal-alkoxide/sol-gel route. Preliminary X-ray diffraction study of the compounds confirmed the formation of single-phase tetragonal compounds. Scanning electron-microscopic (SEM) study of pellet samples of PLBZT shows uniform distribution of grains (spherical) throughout the sample surfaces. Detailed studies of dielectric parameters (dielectric constant, tangent loss) of PLBZT as a function of temperature (30 to 450°C) at 10 kHz reveal that the compounds have diffuse phase transitions. Large variation (first increase and then decrease) in dielectric constant and shift of transition temperature towards higher temperature side with increasing Bi concentration was also observed in PLBZT. The nature of variation of dc resistivity shows that the titled compounds have negative temperature coefficient of resistance (NTCR). Pyroelectric coefficient of the PLBZT compound (z = 0.0 to 1.0) increases with increase of Bi content in PLZT. The transition temperature obtained in this study is very much consistent with that obtained from our dielectric studies. Piezoelectric d ₃₃ coefficient of the compound at 100 Hz was found to be 385, 272, 301, 248 and 291 pc/N for z = 0.0, 0.3, 0.6, 0.9 and 1 respectively.     

Structural and dielectric properties of Pb0.91(La,K)0.09(Zr0.65Ti0.35)0.9775O3 ceramics

Potassium-modified polycrystalline samples of PLZT, Pb_0.91(La_{1 – z/3}K_z)_0.09(Zr_0.65Ti_0.35)_0.9775O₃ [z = 0.0, 0.1, 0.3, 0.5, 0.7], were prepared using sol-gel technique. X-ray diffraction (XRD) of these compounds show that they can be formed in single phase at 800 °C. Pellets prepared from the above powders were sintered at 1100 °C. Detailed studies of the dielectric constant () and loss tangent (tan ) of the compounds at different frequencies (400 Hz to 10 kHz) at room temperature (RT) and temperature (RT to 350 °C) suggest that the compounds undergo ferroelectric phase transition of diffuse-type on increasing K-concentration. Analysis of diffuseness of these compounds gives a value close to 2, which indicates the presence of higher degree of disorder in PLZT substituted by K. The dielectric constant () is found to increase initially and then to decrease with increasing K concentration.     

Rate of heating and sintering temperature effect on the electrical properties of Nd ferrite

The real part of the dielectric constant () and the dielectric loss angle (tan ) as well as the ac conductivity of ferrite Mg_1+x Ti _x Nd _y Fe_2–2x–y O₄ 0.1 x 0.9 at fixed Nd concentration of 0.025 were measured at different temperatures as a function of frequencies. The variation of activation energy as a function of the applied frequency was reported. The obtained data were discussed on the basis of the valence exchange between (Fe³⁺, Fe²⁺), (Fe²⁺, Nd³⁺) and (Fe²⁺, Ti⁴⁺). Also the effect of sintering temperature and heating rate of preparation were discussed.     

Changes in valency state of ions in CuMn2O4 at high temperatures

Thin films of copper manganite with three different molar ratios of CuMn viz 11, 12 and 13 have been deposited on quartz plates. The electrical conductivity of these thin films has been studied as a function of temperature. The energy of activation for electrical conduction in these compounds is found to increase from 0.20 eV to about 0.62 eV above 600° K. Differential thermal analysis of bulk sample of copper manganite also shows a small endothermic change at 600° K, while thermogravimetric analysis does not show any change in weight. It has been concluded from these results that the stable form of the ionic configuration of copper manganite at low temperatures, i.e. Cu¹⁺[Mn³⁺Mn⁴⁺]O₄ changes at high temperatures to Cu²⁺[Mn₂ ³⁺]O₄     

Micro-structural,dielectric, ferroelectric and piezoelectric properties of mechanically processed (Pb<Subscript>1−x</Subscript>La<Subscript>x</Subscript>)(Zr<Subscript>0.60</Subscript>Ti<Subscript>0.40</Subscript>)O<Subscript>3</Subscript> ceramics

In this work, (Pb_1?xLa_x)(Zr_0.60Ti_0.40)O₃ (PLZT x/60/40, x?=?at.%) ceramics were prepared by using high energy mechanical ball milling followed by cold isostatic pressing (CIP), investigated for their micro-structural, dielectirc, ferroelectric and piezoelectric properties. Mechanical activation results in the highly reactive nature of the nano size milled PLZT powders, which enables the partial perovskite phase formation, confirmed by room temperature XRD patterns. CIP leads to a higher density with a closely packed dense microstructure of sintered PLZT ceramics shown in SEM images. The grain size of PLZT x/60/40 ceramics was found to be decreasing with increasing La³⁺ content. The highest relative density of ~?97% was found to be for PLZT 8/60/40 ceramics with grain size of ~?1.35 µm. The PLZT 8/60/40 system also shows the highest dielectric constant of ~?1976, remnant polarization of 29.1 µC/cm², piezoelectric coefficients (d₃₃?\(~ \cong ~\)?570 pC/N, g₃₃?\(~ \cong ~\)?28.03?×?10^?3 Vm/N) and electromechanical coupling factors (k_p?=?k₃₃?=?64.1% and k₃₁?=?54%). The elastic compliances for the PLZT x/60/40 ceramics were also obtained.     

Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

The electrical properties and internal friction in (40–x)Fe₂O₃·xNa₂0.60P₂O₅ glasses were measured. Two or three peak on internal friction were observed in the temperature range of –100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na⁺ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na⁺ion and the hopping of electrons between Fe²⁺ Fe³⁺. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.     

Nd2[MoC2] and RE2[WC2], RE=Ce, Pr, Nd: New carbometalates with Pr2[MoC2] structure type

Four new ternary rare-earth-metal carbometalates, Nd₂[MoC₂] and RE₂[WC₂] with RE=Ce, Pr, Nd, have been synthesized by argon arc melting and subsequent heat treatment at 1170 K for 30 days. They crystallize with the Pr₂[MoC₂] structure type with isolated C⁴⁻ species and are typical carbometalates with (i) low metal-to-carbon ratio, (ii) tetrahedral coordination of the transition metals (T) by carbon, and (iii) a polyanionic network . According to resistivity measurements the compounds are bad metals. Volume chemistry and magnetic susceptibility measurements indicate Pr³⁺, Nd³⁺, and Ce⁴⁺ species, respectively. In the latter case, the additional electron is not transferred to the polyanionic network, instead it mainly populates the Ce partial structure.     

Cation distribution of the system CuAlxFe2−xO4 by X-rays and Mossbauer studies

The structural and Mossbauer spectroscopy studies have been performed on the spinel solid solution series CuAl _x Fe_2–x O₄ (0.0 x 1.0). All the compounds with 0.0 x 1.0 crystallised with cubic spinel structure. Lattice constant values calculated from XRD analysis were found to decrease on increasing x, linearly obeying Vegard's law. The X-ray intensity calculations indicated that Cu²⁺ prefers to occupy octahedral (B) site, where as Al³⁺ ions replace Fe³⁺ ions from both tetrahedral (A) and octahedral (B) sites. Mossbauer spectra at room temperature display magnetic sextets corresponding to A and B-sites superimposed on each other. The data shows that Al-possesses greater preference for B-site compared to A-site, and iron exists in high spin ferric Fe³⁺ state. The hyperfine fields for both A and B-sites decrease with increasing x. The cation distribution calculated from X-ray intensity data agrees with the Mossbauer results.     

Microstructure, dielectric and electromechanical properties of PLSZFT nanoceramics for piezoelectric applications

This investigation highlights the influence of isovalent Sr²⁺ on acceptor Fe³⁺ modified PLZT for microstructure and its effect on dielectric and piezoelectric properties [Pb_0.985−yLa_0.015Sr_y][(Zr_0.538Ti_0.462)_0.985Fe_0.015]O₃ where y = 0, 0.5, 1.0, and 1.5 mol% nanocrystalline solid solutions near morphotrophic phase boundary were synthesized by solid state reaction method. X-ray diffraction patterns indicated that Sr increment resulted in strong tetragonality. Grain size and apparent density enhanced up to y = 1.5 mol%. TEM studies indicated that average particle size ranged from 23 to 68 nm. PLSZFT compositions attained optimum ε_RT, d₃₃, and k_p at y = 1.5 mol%, respectively which could be suitable for possible piezoelectric applications. The influence of grain size on dielectric and piezoelectric properties are reported.     

Superconductivity and spin correlation study by Fe3+ - ESR in (La1−xSrx)2Cu1−yFeyO4−z

Fe³⁺-ESR measurements are carried out for the samples of (La_1–xSr_x)₂Cu_1–yFe_yO_4–z. Peak-peak width H_pp of the signals decreases with falling temperature until minimum value and rises sharply with further decreasing temperature, which is approximated by H_pp = C₀ +C₁/T + BT. The H_pp behavior at high temperature and at low temperature can be analyzed by Korringa mechanism and slowing down of Fe₃₊ spin fluctuation, respectively. From the analysis of coefficient B's of Korringa terms, C₀ and g-shift, it is revealed that the magnetic interaction of Fe³⁺ with hole carriers and Ce²⁺ spins depends strongly on hole density.     

The role of drying-control chemical additives on the preparation of sol-gel derived PLZT thin films

Films of Pb _x/100La _x/100(Zr _y/100Ti _z/100)_1–x/400O₃ with x=8, y=65 and z=35 (PLZT(8/65/35)) with a single perovskite structural phase were successfully prepared by using drying-control chemical additives in sol-gel processing followed by rapid thermal annealing at 600 °C for only 1 min on Si(Pt) substrates. The roles of the drying-control chemical additives ethylene glycol and formamide in the gel preparation were studied. The hysteresis loop of PLZT(8/65/35) thin film was measured. The remanent polarization and coercive field were found to be about 1.3 C cm^–2 and 15 kVcm^–1, respectively.     

Growth and fatigue properties of pulsed laser deposited Pb1 − x La x (Zr y Ti z )O3 thin films with [0 0 /] preferred orientation

Growth of [0 0 /] preferentially oriented Pb_{1 - x} La _x (Zr _y Ti _z ) O₃ (PLZT) thin films was carried out by using targets of either tetragonal or rhombohedral structure. The tetragonal films grew in a similar manner to the rhombohedral films. Both the substrate temperature (500 or 550 C) and oxygen pressure (0.1 mbar, 10 Pa) required stringent control in order to deposit [0 0 /]-textured PLZT thin films. The ferroelectric and fatigue properties were examined.The films deposited on YBa₂Cu₃O_{7 - x} and CeO₂ coated silicon (YBCO/CeO₂/Si) substrates possessed substantially lower remanent polarization than those grown on YBCO coated SrTiO₃ (YBCO/STO) substrates; this is ascribed to inferior crystallinity of the PLZT/YBCO/CeO₂/Si films. The remanent polarization of tetragonal PLZT films was degraded insignificantly up to 10⁸ polarization switching cycles, whereas that of rhombohedral PLZT films was already reduced to 80% of the initial value after 10⁸ cycles. Low endurance of rhombohedral films was ascribed to the periodic stress induced when the inclined spontaneous polarization vector (P = [111]) switched. On the other hand, high endurance of tetragonal films was explained by the fact that the spontaneous polarization vector (P = [001]) lies along the film's normal such that switch cycles cause no lateral stress.     

Advanced ceramics: Combustion synthesis and properties

Fine-particle ceramic powders such as chromites, manganites, ferrites, cobaltites, aluminas (α-Al₂O₃, Cr³⁺/Al₂O₃, zirconia-toughened alumina, mullite and cordierite), ceria, titania, zirconia (t, m, c and PSZ), dielectric oxides (MTiO₃, PZT and PLZT) as well as highT _c cuprates have been prepared by the combustion of redox compounds or mixtures. The combustion-derived oxide materials are of submicron size with a large surface area and are sinteractive.     

Effect of Ca Substitution on the Superconductivity of La2.5Y0.5CaBa3(Cu0.88Fe0.12)7Oz

The structural and superconducting properties of single-phase La_2.5–y Y_0.5Ca_1+y Ba₃ (Cu_0.88Fe_0.12)₇O _z (LYCaBCuFe) (y= 0.0–1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T _c ^R=0 shows a marginal increase from 31 K to 37 K for y = 0.0–0.21 and thereafter it decreases with increasing y leading to zero T _c ^R=0 at y 0.84. This shows that the suppression of T _c from 80 K to 31 K by Fe doping at x = 0.12 La_2.5Y_0.5CaBa₃(Cu_1–x Fe _x )₇O _z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.     

Influence of cerium substitution on structural,magnetic and dielectric properties of nanocrystalline Ni–Zn ferrites synthesized by combustion method

Nickel–Zinc (Ni–Zn) ferrites substituted by cerium (Ce) and having the chemical composition Ni_0.5Zn_0.5Ce _x Fe_2?x O₄ (x?=?0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) were synthesized by combustion method using the organic fuel urea as reducing agent. The effects of cerium substitution on the structural, magnetic and dielectric properties of Ni–Zn compounds have been evaluated. X-ray diffraction patterns indicate that the Ni_0.5Zn_0.5Ce _x Fe_2?x O₄ crystallizes into cubic spinel structure initially and secondary phase emerged along with main spinel phase when the Ce³⁺ content is increased. The elemental composition analysis confirms the stoichiometric presence of expected elements in the samples. Scanning electron microscope and high-resolution transmission electron microscope images reveal the nature of grain growth and the particle size of the synthesized samples. Fourier transform infrared spectroscopy confirms the formation of spinel phase and predicted the shifting of bands corresponding to Fe–O vibrations towards higher wavenumbers compared to undoped Ni–Zn ferrite. Magnetic characterization studies reveal that the substitution of Ce³⁺ into the Ni–Zn ferrite leads to a significant change in saturation magnetization and coercivity values. A plot of dielectric constant (?′) versus applied electrical frequency measured at room temperature shows the normal dielectric behavior of the spinel ferrites. The introduction of Ce³⁺ rare earth ions into Ni–Zn ferrites samples is found to affect the values of both dielectric constant and AC conductivity.     

Electrical transport as a function of temperature in hexacyanoferrate complexes

The electrical conductivity as a function of temperature and the current–voltage dependences of potassium and nickel hexacyanoferro and ferri complexes, have been determined. Charge transfer via the electron delocalization along overlapping d_z ² orbitals of the iron to * orbitals of the ligands (–CN) as well as the ionic conduction via Fe²⁺, Fe³⁺, K⁺, and Ni²⁺ cations are considered as the main sources participating in the conduction processes. The energy gaps, as calculated from the observed maximal absorption wavelengths of ultraviolet and visible spectra, and the activation energies for the free carriers, from the temperature dependence of the electrical conductivity measurements, are consistent with those of semiconductor materials.     

Structural,transport and infrared studies of oxidic spinels Zn1−xNixFeCrO4

X-ray, electrical conductivity and IR studies for the system Zn_1–x Ni _x FeCrO₄ were carried out. All the compounds, 0 x 1 showed cubic symmetry. X-ray intensity calculations and IR studies indicate the presence of Zn²⁺ at tetrahedral sites, Ni²⁺ and Cr³⁺ at octahedral sites, and Fe³⁺ ions are equally distributed at both the sites. Activation energy and thermoelectric coefficient decreases with the increasing values ofX. All the compounds exhibit P-type semiconductivity which may be due to transfer of Fe³⁺ ions from B-site to A-site creating holes. The electrical resistivity temperature behaviour obeys the relation= ₀ exp (E/KT). The mobility of holes as calculated from IR and conductivity data is of the order of 10^–9 cm² V sec^–1. The probable ionic configuration for the system is suggested to be Zn _1–x ²⁺ Fe _x ³⁺ [Fe _1–x ³⁺ Ni _x ²⁺ Cr³⁺] O ₄ ^2– .     

Overlapping Large Polaron Conductivity Mechanism and Dielectric Properties of Al<Subscript>0.2</Subscript>Cd<Subscript>0.8</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> Ferrite Nanocomposite

In this work, the conduction and dielectric properties of Al_0.2Cd_0.8Fe₂O₄ ferrite nanoparticle, which was synthesized by a co-precipitation method, were investigated. Experimental data were taken from 20 Hz to 10 MHz and from 293 to 613 K. AC conductivity of the sample was analyzed within the framework of the overlapping large polaron tunneling (OLPT) mechanism. DC conductivity behavior fits the classical Arrhenius-type conductivity in the examined temperature range. Electrical properties of the material sample have been studied using an impedance spectroscopy technique. The effect of frequency and temperature on dielectric constant (ε ^′), dielectric loss (tan ??), and impedance (Z′ and Z′′) has been discussed in terms of hopping of charge carriers between Fe²⁺ and Fe³⁺ ions. According to results, a relaxation process fits the Cole–Cole model.     

Investigation of structural transport and magnetic properties of the system Li0.25Cu0.5Fe2.25- x Al x O4

Experimental data on X-ray electrical conductivity, thermoelectric coefficient, magnetic hysteresis and infrared absorption spectra of the system Li_0.25Cu_0.5Fe_2.25–x Al _x O₄ are presented. All the compounds, 0x2.25, showed cubic symmetry. Lattice constant values progressively decreased on increasing the Al³⁺ content. X-ray intensity calculations, magnetic hysteresis and infrared spectroscopy studies indicated the presence of Li⁺, Al³⁺ and Fe³⁺ at tetrahedral and octahedral sites, while Cu²⁺ is present only at the octahedral site. The activation energy and threshold frequency increased with increasing values ofx. The compounds withx1.50 aren-type, and those withx2.0 arep-type semiconductors. Magnetic hysteresis indicated that compounds withx1.50 are ferrimagnetic, and those withx2.0 are antiferrimagnetic. High coercive force,H _c, values and remanence ratios (J _R/J_S) showed that all the compounds exceptx2.0 exhibit single-domain behaviour. The probable ionic configuration for the system is suggested as Li _0.15 ⁺ Al _0.5 ³⁺ Fe _0.35 ³⁺ [Li _0.1 ⁺ Cu _0.5 ²⁺ Fe _0.4 ³⁺ Al³⁺]O ₄ ^2– .     

Microstructure and electrical characterisations of K-modified PLZT

Potassium-modified PLZT [Pb_0.92(La_{1 – z}K_z)_0.08(Zr_0.60Ti_0.40)_{0.98 + 0.04z}O₃ (z = 0.0, 0.1, 0.3, 0.5, 0.7)] ceramics were synthesised using sol-gel technique. Preliminary structural and microstructural parameters were determined using XRD, SEM and TEM techniques. Detailed studies of dielectric properties at 10 kHz in a wide temperature range suggest that the compounds have diffuse phase transition of second order. Studies of spontaneous polarisation, pyroelectric and piezoelectric properties yielded data for devices.