Concentration phase transitions in Li x Na1 − x Ta y Nb1 − y O3 solid solutions

The ferroelectric-antiferroelectric concentration phase transitions in solid solutions of Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃, which are promising environmentally friendly (lead-free) ferropiezoelectric materials, are studied by means of Raman spectroscopy.     

Piezoelectric properties of tetragonal single-domain Mn-doped NBT-6 %BT single crystals

We report a study of properties of Mn-doped NBT-6 %BT single crystals. We show that tetragonal single-domain states can be stabilized by poling along a [001] direction. For carefully prepared crystals, the piezoelectric coefficient \(d_{33}\) can reach 570 pC/N. When poled along non-polar directions, the crystals exhibit ferroelectric domain structures consistent with tetragonal micron-sized domains, as revealed by optical observation and Raman spectroscopy. The multidomain crystals have lower \(d_{33}\) values, 225 and 130 pC/N for [011] and [111]-oriented crystals, respectively. This trend is commented on from a domain-engineering perspective.     

Microscopic magnetic properties of (V1−xTix)2O3 near the phase boundary of the metal–insulator transition

Magnetic susceptibility (χ) and ⁵¹V NMR have been measured in (V_1−xTi_x)₂O₃ near the phase boundary of the metal–insulator transition. It is established that the transition from antiferromagnetic insulating (AFI) to antiferromagnetic metallic phases near x_c≈0.05 is not quantum critical, but is discontinuous with a jump of the transition temperature. In the AFI phase at 4.2 K, we observed the satellite in the zero-field ⁵¹V NMR spectrum around 181 MHz in addition to the ‘host’ resonance around 203 MHz. The satellite is also observable in the paramagnetic metallic phase of the x=0.055 sample. We associated the satellite with the V sites near Ti, which are in the V³⁺-like oxidation state, but has different temperature dependence of the NMR shift from that of the host V site. The host d-spin susceptibility for x=0.055 decreases below ∼60 K, but remains finite in the low-temperature limit.     

Synthesis and electrochemical properties of Li8 − x Zr1 − x Nb x O6 solid solutions

New lithium-conducting solid solutions based on lithium orthozirconate have been synthesized by mutual doping of the related structures Li₈ZrO₆ and Li₇NbO₆. The main factor determining the increase in the electrical conductivity of the Li_{8 ? x} Zr_{1 ? x} Nb _x O₆ solid solutions is the formation of lithium vacancies in the tetrahedral and octahedral layers. The practical stability of the Li_{8 ? x} Zr_{1 ? x} Nb _x O₆ ceramics to metallic lithium has been studied.     

Effect of pressure on electrical properties of SnS x Se1−x single crystals

The single crystals of tin monosulphoselenides in the form of a series SnS _x Se_1?x (where x?=?0, 0.25, 0.50,0.75 and 1) have been grown using the direct vapor transport technique (DVT). The analysis of the X-ray diffraction patterns reveals that all crystals belong to the orthorhombic crystal structure. Hall effect measurements were carried out on grown crystals at room temperature. The optical absorption measurements at room temperature have been carried out for all crystals. The values of the band gap were determined at atmospheric pressure and also calculated at high-pressure. Simultaneous thermoelectric power (TEP) and a.c. resistance measurements up to 8?GPa were carried out. The results of the effect of high-pressure on the electrical resistance of the grown crystals are reported in this paper.     

Investigating ionic mobility in solid solutions of Li x Na1 − x Ta y Nb1 − y O3 via Raman spectroscopy

The ionic mobility in Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions (SSes) is investigated by means of Raman spectroscopy. The average lifetime of an Li⁺ ion in the equilibrium position and the magnitude of the potential barrier are estimated from the temperature dependence of the line width corresponding to the vibrations of Li⁺ cations.     

Concentration-phase transitions in solid solutions Li x Na1 − x Ta0.1Nb0.9O3, Li0.12Na0.88Ta y Nb1 − y O3, and NaTa y Nb1 − y O3 and their manifestations in Raman spectra

Using the Raman-spectroscopy method, we have studied concentration-phase transitions in the solid solutions Li _x Na_{1 ? x} Ta_0.1Nb_0.9O₃, Li_0.12Na_0.88Ta _y Nb_{1 ? y} O₃, and NaTa _y Nb_{1 ? y} O₃ (x = 0?0.16, y = 0–1). It has been revealed that, for the solid solutions Li _x Na_{1 ? x} Ta_0.1Nb_0.9O₃ and Li_0.12Na_0.88Ta _y Nb_{1 ? y} O₃, the concentration-phase transition is a transition between the ferroelectric and antiferroelectric states. It is accompanied by the disappearance from the spectrum of a line that corresponds to stretching bridge vibrations of oxygen atoms along the polar axis, which is forbidden by selection rules in the centrosymmetric phase, and by splitting into two components of a line that corresponds to librational vibrations of oxygen octahedra as a whole, which can be caused by doubling of the unit cell in the antiferroelectric phase. Manifestation and variation of intensities of lines with frequencies 860–873 and 900–905 cm^?1 upon variation of the concentration of tantalum for solid solutions Li_0.12Na_0.88Ta _y Nb_{1 ? y} O₃, and NaTa _y Nb_{1 ? y} O₃ is caused by the formation of polar clusters in the medium, which is centrosymmetric in general due to disordering in the sublattice of niobium and tantalum.     

Small-inelastic-strain rate spectrum of C60 single crystals near the phase transition at 250–260 K

The temperature spectrum of small-inelastic-strain rates in a vapor-phase-grown C₆₀ single crystal has been measured within the 200–290 K interval with a high-precision strain-rate meter based on a laser interferometer. The spectrum exhibits a strong peak in the region of the phase transition at 250–260 K and a slight strain acceleration at ∼240 K, which correlates well with the calorimetric curve. The first maximum is associated with strain that developes more easily in an fcc than in a primitive cubic lattice, and the second, to the effect on the strain rate of annealing of the defects created with fast crystal heating. Fiz. Tverd. Tela (St. Petersburg) 41, 1115–1118 (June 1999)     

Electron spin resonance study of the dynamic magnetic susceptibility of CuO, Cu1−x Zn x O, and Cu1−x Li x O single crystals

Results are presented of studies of the dynamic magnetic susceptibility of CuO, Cu_1?x Zn _x O (x ≈ 1.5%), and Cu_1?x Li _x O (x ≈ 1%) single crystals. The orientational dependence of the ESR spectra was investigated at room temperature. The results for CuO are analyzed using a model of a quasi-one-dimensional antiferromagnet (S = 1/2) with anisotropic exchange interaction between Cu²⁺ spins in the chains and exchange coupling between the chains allowing for one-dimensional spin diffusion and spinon excitations. The estimated line width is of the same order of magnitude as the experimental data. Substituting Cu with Zn scarcely alters the spin dynamics of the Cu²⁺ ions, as in weakly diluted magnets. Lithium doping substantially increases the ESR line width and this is attributed to excess holes forming rapidly relaxing spin complexes with copper ions.     

Specific heat of Na1−x V2O5 single crystals

Temperature dependences of the specific heat C and the magnetic susceptibility χ of Na_1?x V₂O₅ single crystals (x=0, 0.01, 0.02, 0.03, and 0.04) are studied. In NaV₂O₅, the transition to the spin-gap state (T _c =34 K) is accompanied by a sharp decrease in χ, while C exhibits a λ-shaped anomaly. At low temperatures, the specific heat of NaV₂O₅ is approximated by the sum of phonon ～T ³ and magnon ～exp(?Δ/T) contributions, which makes it possible to estimate the Debye temperature Θ_D=336 K and the gap in the magnetic excitation spectrum Δ=112 K. With the departure from stoichiometry, the anomalies observed in the behavior of χ and C are spread and shifted to lower temperatures. The low-temperature specific heat of nonstoichiometric samples is determined by the sum of phonon and magnon components and the contribution due to the presence of defects. The values of magnetic entropy characterizing the phase transitions in Na_1?x V₂O₅ are calculated.     

Ferroelectric phase transition of Ba1− x Sr x Ti0.6Zr0.4O3 ceramics

Perovskite type Ba_{1? x} Sr _x Ti_0.6Zr_0.4O₃ (with x = 0.0, 0.1, 0.2, 0.4 and 0.5) ceramics have been synthesized through solid oxide reaction route. The room temperature XRD study suggests the compositions have single phase cubic symmetry. Microstructural studies have shown a step decrease in grain size. The dielectric study reveals that the materials are of relaxor type and undergo a diffuse type ferroelectric phase transition. The diffusivity increases with increase in Sr contents in the studied composition range. The transition temperature decreases with increase in Sr contents due to the decrease in grain size.     

Kinetics of the phase transition in crystals PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–x PbTiO3

The time dependences of the optical transmission, velocity of sound, and elastic constants at room temperature in a number of the [001]-oriented PbIn_1/2Nb_1/2O₃–PbMg_1/3Nb_2/3O_3–x PbTiO₃ single crystals with the compositions lying both far from the morphotropic phase boundary and in its vicinity have been investigated. The analysis of the data obtained has been carried out. It has been shown that, in all the studied crystals, phase transitions induced by an electric field occur in two stages: the first stage is an incubation period associated with a small increase in the polarization of a part of the sample being in the glass phase, and the second phase (after the incubation period τ) is a rapid increase in the polarization and the formation of a long-range order. It has been found that the time τ depends on how close is the temperature of measurements to the Vogel–Fulcher temperature T _f . The closer is the temperature of measurements to the Vogel–Fulcher temperature T _f , the weaker is the electric field required to be applied to the sample in order to induce a ferroelectric phase. It has been demonstrated that the phase state of the studied crystals is unstable, which manifests itself in a strong dependence of the incubation period τ on the time between the annealing of the sample and the beginning of the measurements. The stability of the phase state depends on the PbTiO₃ concentration: an increase in the concentration leads to a significant increase in the stability.     

Phase Structures of （K0.48Na0.52）0.945Li0.055Sb0.05Nb0.95O3 Piezoceramics

The phase structures of lead-free （K0.48Na0.52）0.945Li0.055Sb0.05Nb0.95O3 piezoceramics are studied based on the measurements of ferroelectric and dielectric properties as well as the analyses of x-ray diffraction pattern and energy dispersive spectroscopy. The poled samples exhibit orthorhombic structure whereas the surface and interior for unpoled samples exhibit tetragonal and tetragonal-orthorhombic coexistent structures, respectively. These results are in agreement with the relative permittivity-temperature curves and demonstrate that phase transitions can be induced by Na volatilization and poling process. The remnant polarization Pr measured at 20°C increases continuously with the increase of electric field in the range of 2000-4000V/mm. This indicates that the polymorphic structure is more beneficial to the rotation or reorientation of dipoles than either the orthorhombic or the tetragonal structure. The randomly oriented domains may be the essential reason for the continuous rotation or reorientation and not good thermal stability.     

Synthesis and physicochemical properties of Li2 Me x Zr1 − x O3 − δ (Me = Nb,Ti; x = 0.05, 0.1) solid solutions

Complex lithium metallates Li₂ Me _x Zr_{1 ? x} O_{3 ? δ} (Me = Nb, Ti, x = 0.05, 0.1) with iso-and heterovalent substitutions for Zr⁴⁺ ions in lithium zirconate are synthesized for the first time using a citrate technique. The inclusion of Ti⁴⁺ and Nb⁵⁺ ions in the crystal structure of Li₂ZrO₃ is confirmed by means of X-ray diffraction and NMR. It is shown that in the temperature range of 750–820 K, Li₂Ti_0.1Zr_0.9O₃ solid solution has higher conductivity than phases of undoped lithium zirconate.     

Magnetic and piezoelectric properties of the Bi1 − x La x FeO3 system near the transition from the polar to antipolar phase

The crystal structure, piezoelectric and magnetic properties of the Bi_{1 ? x} La _x FeO₃ solid-solution system near the structural transition between the rhombohedral and orthorhombic phases (0.15 ≤ x ≤ 0.2) have been investigated. The regions of existence of the polar rhombohedral and orthorhombic phases have been determined, and the sequence of structural transitions as a function of the lanthanum ion concentration and temperature has been studied. The maximum piezoelectric signal is found for the solid solution with the composition x = 0.16, which has a single-phase rhombohedral structure. The relation between the type of crystal structure distortions and the increase in the magnetization upon the concentration-driven structural transition from the polar to antipolar phase has been established.     

An origin of infinite range dipole-dipole correlations in soft matrices with off-center impurities: K 1−x Li x Ta 1−y Nb y O 3 and other systems

A model of cooperative behaviour for K 1 m x Li x Ta 1 m y Nb y O 3 (KLTN) and for other disordered systems like ferroelectric relaxors is considered from the point of view of contribution of infinite-range dipole-dipole interactions. It is shown that a local piezoeffect for off-center impurities in crystals with rather high electrostriction is responsible as origin of a infinite-range electric dipole-dipole interaction via elastic fields as well as for a co-existence of ferroelectric and glass-like states with reentrant glass effect.     

Influence of Pr dopant on the dielectric properties and Curie temperatures of Ba1−3x Pr2x Ti0.95Sn0.05O3 (0.01≤x≤0.05) ceramics

Three perovskite-structured ceramic phases Ba_1?3x Pr_2x Ti_0.95Sn_0.05O₃ (BPTS-x) with x=0.01, 0.03, and 0.05 have been synthesized by solid-state reaction method. Obtained BPTS-x ceramics were investigated by X-ray diffraction and dielectric properties measurements. Analysis of all the ceramic samples using X-ray diffraction method at room temperature and its Rietveld refinement inferred rhombohedric structure with the space group $R\bar{3}c$ . The temperature variation of real permittivity gives evidence of the ferroelectric phase transition and of the relaxation behavior. With increasing Pr concentration, the degree of diffuse phase transition was enhanced, and a linear reduction in the transition temperature was produced. The conductivity spectra have been investigated by the Jonscher universal power law (σ(ω)=σ _dc+Aω ^s ) and attributed to hopping conduction mechanism.