Morphotropic Region Research Articles

Magnetoelectric properties of multiferroic ceramic composites

The paper analyzes the influence of hard and soft admixture on the functional properties of multiferroic ceramic composites. Two composite materials via solid-state reaction route were obtained. PZT-type materials (with hard or soft admixture) were selected as the ferroelectric component (90%), and nickel–zinc ferrite as the magnetic component (10%). The influence of the doping type (soft and hard admixture of the ferroelectric composite component) on multiferroic composites’ dielectric, ferroelectric, electromechanical, magnetic, and magnetoelectric properties were analyzed. Microstructural studies revealed the microstructure of composites with the correct distribution of the magnetic component in the ferroelectric matrix, suitable for maintaining both the ferroelectric and magnetic properties of composite materials. Research has shown that using a ferroelectric component as the PZT (from the morphotropic region and doped with the ferroelectrically soft niobium admixture) shows many advantages, positively influencing the functional properties of the multiferroic composite. It ensures effective polarization of the composite sample, obtaining a high magnetoelectric effect, which is required in sensors or magnetoelectric converters. PZT with a hard admixture shows higher stability of physical parameters, but its characteristic property also hinders the effective polarization of the composite sample.

Effect of Li doping on dielectric properties of Na1−xKxNbO3, x = 0.500, morphotropic phase region

Li doped sodium-potassium niobate (Na0.5K0.5)1-yLiyNbO3 ceramic pellets, with y = 0 to 7 (mole) %, were prepared by solid state reaction method with double sintering. With varying lithium content (y), dielectric properties, and X-ray diffraction (XRD) peaks shifting pattern exhibit strong compositional dependence. Among the prepared Composition, a break in XRD peaks shifting tendency, and maximum dielectric constant, electric conductivity were obsreved at the composition with y = 0.06.

Piezoelectric properties of Na1−xKxNbO3, near x = 0.500 morphotropic phase region

Sodium-potassium niobate (Na1-xKxNbO3) ceramic pellets were prepared, near equimolar Na- K composition, by solid state reaction method with double sintering. Remnant polarization, coercive field, polarization current and converse piezoelectric coefficient (d*33) of the prepared samples were measured. The observed properties exhibit strong composition dependence- a morphotropic phase transition type behavior, showing extremal piezoelectric properties for potential lead free transducer applications, at the composition with x = 0.500.

Phase states and electrophysical properties of multicomponent perovskite solid solutions on the base of PMN-PT and PZT systems

Phase diagrams were constructed (at room temperature), the dielectric, piezoelectric, elastic and reversible properties of the Ge-modified [Formula: see text]PbTiO3–[Formula: see text]PbZrO3–[Formula: see text][Formula: see text][Formula: see text]O3 multicomponent system ceramics were studied. The data obtained are compared with the results of studies of solid solutions of basic binary systems, as well as with the results obtained previously for other sections of the system under consideration. A significant increase in the width of the morphotropic region, diffusion of the concentration dependences of the electrophysical characteristics, and an increase in stability under the influence of constant bias fields in the solid solutions of the studied system were established.

Comparative study on heterophase structures in ferroelectric solid solutions based on barium titanate

Heterophase structures are first compared for related perovskite‐type ferroelectric solid solutions that are tin‐modified barium titanate and hafnium‐modified barium titanate with compositions near the morphotropic phase boundary. The studied heterophase structures are interpreted in terms of two models wherein two polydomain phases and a single‐domain interlayer or polydomain and single‐domain phases and a polydomain interlayer coexist at the complete stress relief. The role of the non‐180° domain types and unit‐cell parameters of the coexisting phases is highlighted to show the important link between the phase contents and unit‐cell parameters near the morphotropic phase boundary. A link between the heterophase/polydomain regions and piezoelectric activity of the ferroelectric solid solutions is discussed. Results on the phase contents in the morphotropic region are consistent with experimental data on the aforementioned solid solutions based on barium titanate.

Kinetics of nucleation of thermodynamically ordered ferroelectric phases in PbMg1/3Nb2/3O3–xPbTiO3 crystals with different compositions

The kinetics of electric field-induced nucleation of ordered ferroelectric phases from a mixed glassy relaxor state has been studied in a number of single-crystal (1–x)PbMg1/3Nb2/3O3–xPbTiO3 (PMN–xPT) solid solutions (x = 29, 33, 35%) lying in a morphotropic phase region. It is shown that the formation of these phases and fast establishment of a macroscopic polarization are preceded by some delay time, depending on the electric field strength and temperature. It is found that the monoclinic phase is thermodynamically stable at room temperature in all the compounds in the time (~3000 s) and electric field (~1 kV/cm) ranges under study, whereas the monoclinic phase of the compound with x = 35% transforms, at temperatures near the temperature of the morphotropic phase transition after insignificant time interval of ~100 s, to another stable ferroelectric tetragonal phase.

Phase diagram of the system of (1–х)BiFeO3–x PbFe0.5Nb0.5O3 solid solutions at room temperature

Experimental samples of solid solutions of the (1–x)BiFeO3–xPbFe0.5Nb0.5O3 (0.00 ≤ x ≤ 1.00, Δx = 0.025–0.05) system have been prepared according to the conventional ceramic technology. Their structural and dielectric characteristics have been studied. A phase diagram of the system at room temperature has been plotted taking into account the crystallochemical specificity, spatial inhomogeneity, and structural imperfection of the samples. This diagram is characterized by the presence of solid substitutional and interstitial solutions; the formation of concentration ranges with a dominant role of BiFeO3 and PbFe0.5Nb0.5O3; the presence of five single-phase regions, two regions of coexistence of phase states, and three morphotropic regions; and the formation of six regions with a constant experimental unit-cell volume. Correlations between the structural characteristics and dielectric properties of the ceramics under study have been established.

Structural and electrical characteristics of rhombohedral lead zirconate titanate single crystals

Two PbZr x Ti1−x O3 (PZT) single crystals, from a batch prepared by the flux method, were analysed to assess their chemical composition. The two single crystals were found by electron microprobe analysis to have the chemical compositions PbZr0.60Ti0.40O3 and PbZr0.65Ti0.35O3. X-ray diffraction at −93 °C revealed that both crystals have the R3m space group, which means that the R3m ↔ R3c phase transition is not observed in this composition range for temperatures above −93 °C. The dielectric permittivity was measured along the [001] direction at several frequencies from 1 kHz to 1 MHz, at varying temperatures up to 460 °C, and the parameters of the Curie–Weiss law were determined. The parameters of a thermodynamic model for the rhombohedral phase were determined by fitting the experimental data with the theoretical model. The polarization was calculated as function of the temperature for both crystals and the results were used to observe the order of the phase transition. The polarization increases when the concentration of PZT approaches the morphotropic region from the rhombohedral side. This fact, already observed in ceramic samples, is for the first time reported in single crystals which contributes for the clarification of the maximum of electrical properties in the morphotropic region.

Relaxation currents in morphotropic region of Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ferroelectric ceramics

Studies on the dielectric relaxation currents in the morphotropic region of Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 with x + y + z = 1, x = 0.1 and y = 0.44–0.46 are presented. The measurements have been performed at three poling fields, i.e. (a) 0.02 kV cm−1 that is much lower than the coercive force (8 kV cm−1), (b) 10 kV cm−1, i.e. slightly above the coercive force and (c) much higher field (20 kV cm−1). There were measured transient polarisation and depolarisation currents. For a low poling field, these currents do not differ from each other, but for higher fields the difference increases with increasing poling field. The analysis of depolarisation current data obtained at various temperatures (298–473 K) shows that relaxation time τp varies exponentially with temperature. The activation energies calculated for samples with y = 0.44, 0.45 and 0.46 equals to 0.26, 0.24 and 0.22 eV, respectively. The defect dipole ) complex and the Dissado–Hill double-minimum potential models are proposed to explain the observed relaxation behaviour in Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ferroelectric ceramics.

A new Pb(Lu1/2Nb1/2)O3–PbZrO3–PbTiO3 ternary solid solution with morphotropic region and high Curie temperature

A ceramic ternary system of (1− x − y )Pb(Lu 1/2 Nb 1/2 )O 3 – x PbZrO 3 – y PbTiO 3 (PLuN–PZ–PT) has been prepared by two-step synthetic process and characterized by X-ray powder diffraction and electric measurements. A morphotropic phase boundary (MPB) region has been delimited in the ternary system at room temperature. With the PLuN content increasing, the morphotropic phase boundary region becomes broad as well as the dielectric peak. The best comprehensive piezoelectric properties were achieved at MPB composition 0.42PLuN–0.1PZ–0.48PT, with the piezoelectric coefficients d 33 , the Curie temperature T c , the planar electromechanical coupling factor K p , and the remnant polarizations P r being 367 pC/N, 360 °С, 68% and 35 μС/cm 2 , respectively. The results indicate that the PLuN–PZ–PT ternary ferroelectric material may be a promising candidate for high-power electromechanical transducers that can operate in a large temperature range.

First-principles investigation of the structural phases and enhanced response properties of the BiFeO3-LaFeO3multiferroic solid solution

We present a first-principles study of the Bi${}_{1\ensuremath{-}x}$La${}_{x}$FeO${}_{3}$ (BLFO) solid solution formed by multiferroic BiFeO${}_{3}$ (BFO) and the paraelectric antiferromagnet LaFeO${}_{3}$ (LFO). We discuss the structural transformations that BLFO undergoes as a function of La content and the connection of our results with the existing crystallographic studies. We find that, in a wide range of intermediate compositions, BLFO presents competitive phases that are essentially degenerate in energy. Further, our results suggest that, within this unusual morphotropic region, an electric field might be used to induce various types of paraelectric-to-ferroelectric transitions in the compound. We also discuss BLFO's response properties and show that they can be significantly enhanced by partial substitution of Bi/La atoms in the pure BFO and LFO materials. We analyze the atomistic mechanisms responsible for such improved properties and show that the effects can be captured by simple phenomenological models that treat explicitly the composition $x$ in a Landau-like potential.

Structural features of the formation of La1−x Ca x FeO3−δ (0 ≤x ≤ 0.7) hetero valent solid solutions

A synthesis method with the use of polymer-salt compositions (calcination temperature 800°C) provides the preparation of various solid solutions of a La1−x Ca x FeO3−δ series in the 0≤ x≤ 0.7 range, which belong to the perovskite structure type. A morphotropic phase transition occurs from the orthorhombic perovskite modification (0≤ x ≤ 0.4) to the cubic one (0.5 ≤ x≤ 0.7). A growing number of microdistortions in the perovskite structure and the formation of a microblock structure in the morphotropic phase transition region are observed with increasing degree of calcium substitution for lanthanum. Calcination of solid solutions with x = 0.6 and 0.7 at temperatures above 1000°C in the air or under conditions of reduced oxygen partial pressure (laboratory vacuum of 10−3 Torr) results in the formation of a nanostructured state with coherently grown blocks of perovskite and Grenier phase, which is due to irreversible oxygen loss.

Dispersion of the permittivity of a uniaxial ferroelectric solid solution in the morphotropic region

A phenomenologic al theory of the permittivity dispersion fk(ω) in tetragonal ferroelectrics with polarization directed normally to a selected axis was developed for the first time. The permittivity dispersion was calculated for single-domain single crystals in both symmetry-allowed low-symmetry phases. A simple model is proposed for calculating the permittivity dispersion of solid solutions belonging to the morphotropic region of T-c phase diagrams. This model includes the results obtained for single-domain crystals, which in combination with the special averaging method yield the equality (fk(ω)) = ((fk-1 (ω)))-1.

Morphotropic Region in Na1−xKxNbO3, Between x = 0.17 and 0.18

Pellet samples of Na1−xKxNbO3 (0.12 ≤ x ≤ 0.20) were prepared by solid state reaction method. With varying composition, the observed break in the X- ray diffraction peak shifting tendency, the slope change anomaly in the c/a vs. x plot, and the anomalous change in the dielectric properties identify a morphotropic region in the composition range between x = 0.17 and 0.18.

Compositional range and electrical properties of the morphotropic phase boundary in the Na 0.5Bi 0.5TiO 3–K 0.5Bi 0.5TiO 3 system

We have investigated the Na 0.5Bi 0.5TiO 3–K 0.5Bi 0.5TiO 3 (NBT–KBT) system, with its complex perovskite structure, as a promising material for piezoelectric applications. The NBT–KBT samples were synthesized using a solid-state reaction method and characterized with XRD and SEM. Room-temperature XRD showed a gradual change in the crystal structure from tetragonal in the KBT to rhombohedral in the NBT, with the presence of an intermediate morphotropic region in the samples with a compositional fraction x between 0.17 and 0.25. The fitted perovskite lattice parameters confirmed an increase in the size of the crystal lattice from NBT towards KBT, which coincides with an increase in the ionic radii. Electrical measurements on the samples showed that the maximum values of the dielectric constant, the remanent polarization and the piezoelectric coefficient are reached at the morphotropic phase boundary (MPB) ( ɛ = 1140 at 1 MHz; P r = 40 μC/cm 2; d 33 = 134 pC/N).

Integration and Optimisation of PZT Piezoelectric Thin Films in Micro and Nano Dimensional Structures

We present in this paper a complete study of PZT thin films grown by r.f. sputtering onto platinised silicon substrates; the films are deposited at room temperature and post annealing is necessary to crystallise the PZT in the perovskite phase. The PZT composition (ratio Zr/Ti) is fixed to 54/46, i.e. in the morphotropic region where the piezoelectric activity is a maximum. For a future use in MEMS/NEMS it is imperative to know the intrinsic piezoelectric coefficients of the films; in particular the coefficients are d33, e31 and d31 are the most important to obtain. To determine these we have developed an experimental set-up based upon a commercial laser Doppler vibrometer and specific sample preparation procedures developed in the laboratory. These are necessary so that we do not integrate the substrate contribution with the measurement of the piezoelectric coefficient. The macro-structure of the PZT films is treated in this paper, as well as the micro and nano structure of the thin films and devices. This work has focused on two main objectives: optimisation of the etched processes: IBE (RIE) for micro structure fabrication and FIB for nanostructure and evaluation of the electrical degradations induces by the etching processes. We have optimised the process in order that functional performance is not degraded after etching. Keywords: Piezoelectric, PZT, Thin Films, Structure ( MEMS, &, NEMS), Piezoelectric coefficients

Optical investigations of structural phase transformations in PbMg1/3Nb2/3O3-xPbTiO3 single crystals located at the morphotropic phase boundary

A study has been made of the effect of a dc electric field (0 < E < 4 kV/cm) on the optical transmittance of single-crystal compounds PbMg1/3Nb2/3O3-xPbTiO3 (PMN-xPT) located at the boundaries of the morphotropic region (x = 32.0 and 36.5%) and directly at the center of the morphotropic region (x = 35%). It is shown that, at temperatures close to the morphotropic phase transition point, the electric field induces two phase transitions in PMN-32PT and PMN-35PT crystals and only one phase transition in PMN-36.5PT. The tetragonal (T) phase induced in all three compounds remains stable after the electric field is removed only in crystals with x = 35.0 and 36.5%, whereas the T phase is metastable and transforms into the monoclinic M c phase after the field is switched off in the PMN-32PT crystals lying at the boundary of the morphotropic region on the rhombohedral side. It is found that the electric-field-induced intermediate phase M c in PMN-35PT is inhomogeneous and that M c transforms into the tetragonal phase in a continuous transition. It is suggested that only the presence of a third orthorhombic phase can account for the continuous character of the transition between the M c and T phases in PMN-35PT crystals. The results obtained are interpreted in terms of the Devonshire theory for strongly anharmonic crystals. The E-T phase diagrams are constructed for all the crystals.

High-temperature studies of La1−x SrxFeO3−δ solid solutions using synchrotron radiation

A series of La1−x SrxFeO3−δ samples with a perovskite structure were investigated by high-temperature X-ray analysis using synchrotron radiation. In this series, one can observe a morphotropic phase transition (0.3 ⩽ x ⩽ 0.4) from the orthorhombic (0 ⩽ x < 0.3) to cubic (0.4 < x ⩽ 0.75) modification. The samples from the morphotropic transition region (MTR) at room temperature have a highly disordered microblock structure related to their phase heterogeneity; according to high-temperature X-ray analysis data, this is the result of particle stratification of the high-temperature homogeneous solid solution formed at the temperature of the synthesis (1200°C) in the course of cooling.

Pyroelectric properties of PZT-type ferroelectric ceramics in the morphotropic phase-transition region

The temperature changes in the pyroelectric coefficient of the PZT-type materials synthesized in the morphotropic phase-transition region have been dynamically investigated under different polarization conditions. The temperature ranges of thermodynamic instability of the domain and phase structures after the “high-voltage” polarization have been revealed. The samples undergoing a phase transition into the ferroelectric state in an electric field exhibit enhanced thermal stability of domain structures.

Electric-field-induced phase transitions in &lt;001&gt;-oriented PZN-9PT and PMN-35PT single crystals

Effects of a constant electric field (0 < E < 5 kV/cm) on the optical transmission of 91PbZn1/3Nb2/3O3-9PbTiO3 (PZN-9PT) and 65PbMg1/3Nb2/3O3-35PbTiO3 (PMN-35PT) single crystals belonging to the morphotropic regions of these solid solution systems have been studied. At temperatures close that of the morphotropic phase transition, the applied electric field induces two new intermediate monoclinic phases (Ma and Mc) in PZN-9PT and a single intermediate monoclinic phase in PMN-35PT crystals. In PMN-35PT, the new phase is inhomogeneous; in PZN-9PT, the transition from Ma to Mc has a continuous character. The E-T phase diagrams for both crystals are constructed. The results are interpreted within the framework of the Devonshire theory of strongly anharmonic crystals.