The aim of the work was the synthesis and studies of ceramic samples of the ternary BaTiO3-BaSnO3-PbTiO3 system, which had not been systematically studied before. Thermogravimetric, X-ray diffraction, dielectric and pyroelectric studies were performed on the synthesized samples of (1-x)BaTi1-ySnyO3xPbTiO(3) compositions with 0 <= y,x <= 1. It was found that solid solutions with the perovskite structure are formed throughout the composition region in the system. Concentration regions in which solid solutions of different symmetries are formed have been determined. The results of dielectric and pyroelectric studies show that an increase in BaSnO3 content in samples leads to a change in their dielectric properties from ferroelectric to relaxor ferroelectric, then to properties such as those of dipole glass, and then to the properties of linear dielectrics. The research results are presented in the form of x-T phase diagrams for the entire concentration range of the (1-x)Ba(Ti1-ySny)O-3xPbTiO(3) system.

The search for high-performance, lead-free materials with tailored electromechanical properties is crucial for the advancement of energy harvesting and actuator technologies. While piezoelectric materials offer promising solutions, balancing high piezoelectric response with low dielectric permittivity remains a significant challenge. Recent research has highlighted the potential of “giant” electrostriction as an alternative approach, offering substantial electromechanical responses with more favorable electrical properties. This work investigates the electrostrictive and dielectric properties of non-textured and textured La2Ce2O7 ceramics. Our findings reveal a substantial electrostrictive coefficient [M33 ≈ 10−18 (m/V)2, exceeding conventional electrostrictive materials], coupled with a high effective piezoelectric response (d33eff = 40 pm/V at E = 100 kV/cm) and a high effective piezoelectric voltage coefficient (g33eff = 146–205 × 10−3 Vm/N). Notably, [111]-texturing of La2Ce2O7 significantly reduces dielectric losses, further enhancing its suitability for energy harvesting and actuator applications. The combination of electromechanical and dielectric properties creates conditions for high energy-harvesting performance, comparable to lead-containing ceramics and far superior to lead-free alternatives. Combined with temperature stability and compatibility with Si-based microfabrication, La2Ce2O7 emerges as a promising lead-free alternative for high-performance electromechanical energy conversion applications.

For the first time, ceramics of the Bi2O3-ZnO-Nb2O5 system with high density, homogeneous microstructure and high dielectric parameters (higher by 30% in comparison with traditional ceramic technologies) were obtained by spark plasma sintering. The mechanisms of ceramic frame formation have been studied and technological modes of sintering have been optimized.

Ceramics of a Bi2O3–ZnO–Nb2O5 system (cubic pyrochlore) with homogeneous microstructures, high densities, and high dielectric parameters (30

For over a century, materials science has been focused on comparing magnetism and ferroelectricity, revealing similarities in order types, domains, hysteresis, and responses to external stimuli. The exceptional physical properties of magnets often originate from frustration, which can result from site disorder and lattice geometry. While disordered relaxor ferroelectrics exhibit ultra-high dielectric and piezoelectric properties and fingerprinted behavior similar to spin glasses, ferroelectric-like materials with clear geometrically frustrated states have not been previously identified. Here we introduce a new type of relaxor material, a geometrically frustrated relaxor, exemplified by a Bi2Ti2O7 single crystal with a compositionally ordered pyrochlore structure. Our findings demonstrate canonical relaxor behavior, including dielectric anomalies, dipole freezing, non-ergodicity and a lack of spontaneous phase transitions. Furthermore, we show the emergence of a unique dipole ice state upon cooling, arising from conflicting order parameters related to two mutually exclusive rigid unit modes of Bi4O' tetrahedral rotations. The coexistence of these rotations does not satisfy symmetry constraints, causing geometrical frustration and suppressing the long-range order. The results provide the structural mechanism of geometrical frustration manifestation in Bi-containing pyrochlores, opening up avenues for exploring exotic ground states and advanced functionalities in dielectric materials.

The effect of doping on the chemical and physical properties of semiconductors, alloys, ferroelectrics, glasses, and other substances has been a classic topic in materials science for centuries. Strontium titanate, SrTiO3, is an archetypal perovskite of interest for both fundamental science as quantum paraelectric and numerous outstanding physical properties and applications, including dielectrics, tunable microwave and photovoltaic devices, superconductors, thermoelectrics, potential multiferroics. Its chemical doping with transition metals leads to new functionalities, but intrinsic mechanisms of structural responses, activated by impurities, have not been systematically investigated. Herein, we present the results of a comparative study of the crystal structure, vibrational spectra, and dielectric properties of SrTiO3:M (M = Mn, Ni, and Fe, 2 at%) single crystals. It is shown that impurities constitute a different tendency to off-centering and the formation of dipoles: Mn and Fe atoms are shifted from the center of the oxygen octahedron, while Ni atoms remain on-centered. As a result, small chemical doping has a dramatic effect on the dielectric response through various structural mechanisms, including the pseudo Jahn-Teller effect, the first-order Jahn-Teller effect, and defect-induced distortion. These findings open up fundamentally new possibilities for the practical solution of a difficult problem: controlling the dielectric responses of quantum paraelectrics by choosing the type of chemical additive.

The results of dielectric hysteresis loops and dielectric permittivity studying of 0.725NaNbO3–0.20KNbO3–0.075CdNb2O6 ceramics in strong (5–40 kV · cm–1) and weak (0–0.3 kV · cm–1) alternating electric field are presented. The parameters of the reversible and irreversible contributions to the dielectric permittivity are determined. Based on the Preisach model, a diagram of the density of domain switching is constructed. It is shown that the distribution function of domains over local coercive fields is characterized by a sharp peak, which indicates a high degree of homogeneity of the domain structure.

The new xMnAs/(1 − x)PMN–PT (x = 0.2, 0.3) multicaloric composites, consisting of the modified PMN–PT-based relaxor-type ferroelectric ceramics and ferromagnetic compound of MnAs were fabricated, and their structure, magnetic, dielectric properties, and caloric effects were studied. Both components of the multicaloric composite have phase transition temperatures around 315 K, and large electrocaloric (~0.27 K at 20 kV/cm) and magnetocaloric (~13 K at 5 T) effects around this temperature were observed. As expected, composite samples exhibit a decrease in magnetocaloric effect (<1.4 K at 4 T) in comparison with an initial MnAs magnetic component (6.7 K at 4 T), but some interesting phenomena associated with magnetoelectric interaction between ferromagnetic and ferroelectric components were observed. Thus, a composite with x = 0.2 exhibits a double maximum in isothermal magnetic entropy changes, while a composite with x = 0.3 demonstrates behavior more similar to MnAs. Based on the results of experiments, the model of the multicaloric effect in an MnAs/PMN–PT composite was developed and different scenario observations of multicaloric response were modeled. In the framework of the proposed model, it was shown that boosting of caloric effect could be achieved by (1) compilation of ferromagnetic and ferroelectric components with large caloric effects in selected mass ratio and phase transition temperature; and (2) choosing of magnetic and electric field coapplying protocol. The 0.3MnAs/0.7PMN–PT composite was concluded to be the optimal multicaloric composite and a phase shift ∆φ = −π/4 between applied manetic fields can provide a synergetic caloric effect at a working point of 316 K.

Multicomponent ceramics based on PbMg1/3Nb2/3O3-PbTiO3 system were studied using X-ray diffraction at high electric fields. It was shown that electric field induced phase transition from initial pseudocubic phase to tetragonal one occurs at E > 5 kV/cm. Analysis of the intensities of the 200 X-ray peak components reveals the parameters of the tetragonal unit cell (c = 4.036 & ANGS; and a = 4.021 & ANGS;) and the degree of preferential domain orientation (& AP; 35%) at E = 12 kV/cm. The results of X-ray diffraction studies are in a good agreement with the field-induced behavior of the macroscopic responses: strain, polarization, and dielectric permittivity.

Systematic study of the terahertz soft -mode in SrTiO3: M thin (150 nm) films doped (2 at%) with transition metals M = Mn, Fe, Ni, Co is performed at frequencies 7-1000 cm(-1) and temperatures 5-300 K. The soft mode dielectric strength and frequency follow the Barrett -like temperature behaviours with unusually high quantum temperatures and large in magnitude negative Curie temperatures, indicating strong destabilization of the ferroelectric state due to a combined effect of quantum fluctuations, dead layers at the boundaries of crystallites, misfit strains within crystallites and disorder induced by doping. Dopant-dependent variation in the asymmetry of the Fano resonance describing coupling of the TO2 phonon and continuum states of polarization fluctuations is observed suggesting presence of polar nanoregions in the films. Clear correlation between the asymmetry parameter and the Barrett quantum temperature is observed that highlights the complex character of the local structure -dielectric properties relationships in the films.

Based on the symmetry related concept of the group theory we predict two structures with enan-tiomorphic space groups PI43 and PI41. These phases arise as a result of spin ordering on 16d Wyckoff position in crystals with space group Fd3m. It is shown that PI43 and PI41 hypothetical magnetic structures are multiferroics of type II. The ferroelectric polarization emerges through a mechanism of the hybrid improper ferroelectricity allowing trilinear coupling of polarization and two other antiferromagnetic order parameters. In addition to improper ferroelectricity, the symmetry analysis proves the possible coexistence of other improper ferroic orders including orbital, ferroelastic, ferroelastoelectric, ferrobielastic, optical, ferroaxial, ferrotoroidic, gyrotropic and other crystal freedom degrees.

The family of crystals with a pyrochlore lattice, including pyrochlores, spinels, and Laves phases (C15) is a fertile playground for the discovery and scientific study of exotic magnetic properties as well as search for new technological applications. In this work a possible magnetically long-range ordered phases derived from the archetypical pyrochlore lattice were studied within the Landau phase transition theory. A group-theoretical analysis reveals the existence of 20 low symmetrical phases, generated by the magnetic order parameters associated with the center of the Brillouin zone. For each of these phases, the symmetry-related magnetic and structural parameters were determined and discussed in detail. We extend this analysis by means of the thermodynamic theory: on the ground of the sixth-degree thermodynamic potential phase diagrams of the spin-ordered pyrochlore-based magnets are constructed in the exchange approximation. It is shown that an essential feature of all studied phase diagrams is the existence of singular elements: multiphase points, multicritical points of different types, lines of phase transitions of both the first and second order.

A comparative study is performed of Bi4Ti3O12-based high-temperature ferroelectric ceramics fabricated with three different types of sintering. The dependences of the microstructure, dielectric and piezoelectric properties of the ceramics on the types of sintering are established. It is shown that ceramics sintered with hot pressing have the best combination of functional characteristics.

Dielectric spectra of SrTiO 3 and SrTiO 3 :Mn single crystals have been studied in the frequency range of 10‒3000 cm –1 and in the temperature range of 5–297 K using time-domain terahertz spectroscopy and Fourier-transform infrared spectroscopy. A comparative analysis of the experimental results made it possible to detect a significant broadening of the absorption lines corresponding to the Slater and Last phonon modes, while the parameters of the Axe mode when replacing Ti with Mn (2 at %) stay invariant. This effect is associated with an enhance in structural disorder in the cation subsystem (B-sublattice) of the SrTiO 3 crystal. It has been established that doping with Mn ions reduces the antiferrodistortive phase transition temperature by about 20 K, but hardly affects the character of the temperature dependence of the parameters of a ferroelectric soft mode at temperatures of about 60–297 K. It has been found that an additional excitation with the frequency below the frequency of the ferroelectric soft mode should be taken into account for an appropriate model description of the dispersion of the permittivity of SrTiO 3 :Mn in the terahertz frequency range. The results obtained in this work indicate that dielectric relaxation in the SrTiO 3 :Mn crystal is due to thermally activated hops of Mn atoms between displaced (noncentral) crystallographic sites; i.e., the mechanism of radiofrequency relaxation in SrTiO 3 :Mn is hopping rather than polaronic, which is also actively discussed in the literature.

Results are presented from a group-theoretical analysis of phase transitions in LiRh2O4. It is found that the critical irreducible representation inducing phase transitions and multiorder in this substance is eight-dimensional representation k11τ5 ( Γ_3^ + ) + k10τ2 (X4). It is shown that the multiorder and structural mechanism of the formation of the tetragonal phase of lithium rhodonite are related to displacements of oxygen atoms, the tilts of [RhO]6 octahedra, and the ordering of rhodium t2g orbitals.

Based on the combined group-theoretical and crystallographic approach, the possible perovskite-derived structures of proper and improper ferroelastics were established. The crystallographic analysis of the Wyckoff position splitting in the low-symmetry proper ferroelastic phases shows the absence of any non-ferroelastic degrees of freedom that reduces the possibilities of structural relaxation. Group-theoretical analysis reveals that tilts of anionic octahedra, as the most common type of structural distortions in perovskites, are closely related to ferroelastic strains, except for the phase with tilt pattern a (+) a (+) a (+). For such kind of improper ferroelastics, the simplest classification was suggested based on the relationships between the coupled order parameter (tilts of octahedra) and the lattice strain components.

Results are presented from experiments on the dielectric hysteresis loops and relative dielectric permeability of 0.725NaNbO 3 –0.20KNbO 3 –0.075CdNb 2 O 6 ceramics in strong (5–40 kV cm –1 ) and weak (0–0.3 kV cm –1 ) alternating electric fields. The parameters of reversible and irreversible constituents of contributions to the dielectric permeability are determined. A diagram of domain switching densities is plotted using the Preisach model. It is shown that the function of the domain distribution over local coercive fields is characterized by a sharp peak, testifying to the strong homogeneity of the domain structure.

Hexagonal ferrites with the formula SrxBa(1−x)Fe12O19 (x = 0; 0.3; 0.5; 0.7; and 1) were prepared using the citrate method. The main feature of this synthesis is a relatively low calcination temperature of 700 °C. An X-ray diffraction study revealed a single-phase material. According to SEM, the particles were 50−70 nm in diameter. The Curie temperature of the samples that were determined using the DSC method varied in a very narrow range of 455−459 °C. Analysis of the magnetic hysteresis loops obtained at 300 K and 50 K indicated all samples as magnetically hard materials in a single-domain state. The maximal magnetic characteristics encompass strontium hexaferrite. The terahertz spectra of complex dielectric permittivity and the spectra of infrared reflectivity were measured at room temperature in the range of 6–7000 cm−1. The obtained broad-band spectra of the real and imaginary parts of permittivity reveal significant changes associated with structural distortions of the (Sr,Ba)O12 anti-cuboctahedron caused by the substitution of Ba2+ with Sr2+ in the same crystallographic positions.

Spin ordering in the geometrically frustrated magnetic materials with pyrochlore lattices is a key player in the emergent phenomena in modern condensed matter. A possible spin-ordered phases derived from the archetypical pyrochlore lattice were studied within the Landau conception of order parameter (OP) for case wavevector k 1/4 (0,0,0) associated with the center of the Brillouin zone of space group Fd3m: The existence of 20 low-symmetry types of spinordered phases is established. For each phase space group and set of proper and improper OPs are defined. Only one phase generated by irrep m Gamma(+)(2) is not ferroelastic. The fundamental feature of spinordered phases in the pyrochlore lattices is that all remaining 19 phases found are improper ferroelastics. The U5thorn (a,a,a) shear deformation, involved in the formation of phases with space groups R3m0, R3m0, and R3, is proved to be the only one that contributes to the formation of these rhombohedral distorted spin-ordered phases. Other types of shear deformations Gamma(+)(5)(a,0,0) and Gamma(+)(2)(a,b,b) are always cooperate with some of the Gamma(+)(3)deformations at the formation of spin-ordered pyrochlores.