Vladimir Borisovich Shirokov

Controlling ferroelectric phase symmetry through strain engineering is crucial for tailoring polarization topology and functional properties in oxide-based devices. Here, we show that a thin conductive buffer layer can over-ride substrate-induced strain in BaTiO3 (BTO) films on MgO. Although the lattice parameter of MgO(001) would be expected to induce tensile misfit strain, in 500 nm BaTiO3 films the thermal-expansion mismatch dominates,resulting in effective compressive stress upon cooling. Inserting a 50-nm La0.67Sr0.33MnO3 (LSMO) buffer layer reverses the effective strain state from compressive to tensile. Using temperature-dependent polarized Raman spectroscopy, X-ray diffraction, and piezoresponse force microscopy, we reveal an unconventional phase sequence upon cooling: paraelectric → orthorhombic (aa-phase, ∼407 K) → monoclinic (r -phase, ∼300–345 K), characterized in-plane and tilted polarization components. The LSMO layer not only serves as a bottom electrode but also modifies the strain state, while interfacial charge redistribution induces a built-in electric field, evidenced by self-polarization and asymmetric PFM hysteresis. These findings highlight the critical role of conductive buffer layers in controlling ferroelectric symmetry and enabling oxide heterostructures with tailored polarization textures for low-power spin- tronics, tunable microwave devices, and neuromorphic computing.

The widespread use of ferroelectric materials in tunable electronic devices is often limited by energy dissipation at domain walls in the ferroelectric state. Low dielectric losses and high tunability can be achieved by operating the material in the paraelectric phase under an external electric field. Under these conditions, a domain-free, field-stabilized ferroelectric-like state can be induced, particularly near phase boundaries or multicritical points. We investigate the electric-field control of dielectric and piezoelectric properties in paraelectric Pb _x Sr _{1− x} TiO ₃ (PST) thin films epitaxially constrained on cubic substrates. Using a Landau–Ginzburg–Devonshire thermodynamic potential that incorporates both polarization and octahedral tilting as coupled order parameters, we construct the room-temperature (300 K) phase diagram in the misfit strain–composition ( u _m – x ) plane. Within the paraelectric region, we analyze the system’s responseunder a perpendicular electric field ( E _z = 100 kV cm ⁻¹ ), which induces a uniaxial, domain-free ferroelectric-like state, often referred to as a ‘forced’ ferroelectric. We calculate the field-dependent permittivities ( ε 33 , ε 11 ) and induced piezoelectric coefficients ( d i j ,   e i j ) along a path within the paraelectric phase near the adjacent ferroelectric phase boundaries. Our results show a pronounced enhancement of dielectric tunability t ( ε ) and non-zero piezoelectric response in regions near the multicritical point ( u _m ≈ 0, x ≈ 0.138), where the paraelectric phase borders the c -phase (tetragonal, P 4 m m ), r -phase (rhombohedral-like monoclinic, C m ), and aa -phase (orthorhombic, A m m 2 ). The most pronounced effects occur near the boundary with the c -phase, where the out-of-plane polarization mode undergoes softening. These findings indicate that operating PST thin films in the paraelectric phase under an external bias enables low-loss, highly tunable behavior, making them promising candidates for reconfigurable microwave and electronic devices.

Closed channel structures with interfaces formed by p – n junctions, used in high- current electronics, can be formed by the aluminum thermomigration in single-crystal silicon wafers. The equilibrium shape of self-formed channels, depending on material parameters and structure geometry, corresponds to the minimum of the total elastic energy. The contribution of elastic energy to the shape of formed aluminum-doped thermomigration channels in a single-crystal silicon wafer of (100) orientation is studied and presented in this manuscript. It is found by finite element analysis that the minimum of elastic energy is observed in structures where the channel crystal orientation is rotated by an angle of 45 degrees in the crystallographic plane parallel to the substrate surface. At this angle, the structures have a non-zero tilt to the surface normal, with the slope angle depending on the thickness of the channels and the spacing between them.

The electro-optic coefficients of ferroelectric materials were obtained by Landau thermodynamic theory. It is proved that if the permittivity tensor is diagonal, then some ratios of the electro-optical coefficients are equal to the ratios of its diagonal components. The dependence of electro-optic coefficients on the external electric field for single-crystal barium titanate was studied and discussed. It is shown that electro-optic coefficients are rather high for barium titanate due to a non-linear response of dielectric susceptibility to electric field strength.

The excitation of surface acoustic waves (SAWs) on the surface of the ferroelectric film [barium strontium titanate (BST)] located on the dielectric substrate (silicon) was studied theoretically. We found that the most effective SAW excitation takes place when spontaneous polarization occurs in the film plane and the wave propagates along the direction adjacent to the direction of the spontaneous polarization vector. Based on a nonlinear model of phase transitions in solid BST solutions, the dependency of the material constants of piezo-effect equations on the misfit strain with a fixed concentration was obtained numerically. The effect of various misfit strains on SAW characteristics was studied for the film located on single-crystal silicon. It was shown that the effectiveness of SAW excitation increases as the misfit strain nears the boundary of phase transition.

A symmetry-guided approach for designing and tailoring magnetoelectric and multiferroic hexaferrites is proposed. A group-theoretical study of the magnetoferroelectric structures of a hexagonal ferrite was carried out. The results were applied to M-, W- and Z-type hexaferrites. It is shown that the magnetic structure cannot be collinear in the main magnetic phase, with the direction of the magnetic moment along the hexagonal axis. Magnetic sublattices are shown in which cation substitution should lead to the formation of a multiferroic state. A thermodynamic model of a hexagonal ferroelectric ferrimagnet was constructed, in which isostructural phase transitions were observed.