K. G. Abdulvakhidov

Diffuse phase transition in NaNbO3:Gd single crystals

Gd-doping of NaNbO3 crystals leads to gradual diffusion of an antiferroelectric phase transition. Though the permittivity maximum in crystals with a high Gd content is even more diffused than in PbMg1/3Nb2/3O3, its frequency shift is negligible in the (1–100) kHz range. We explain the diffuseness of the phase transition in NaNbO3:Gd within a Landau-type theory that includes the coupling of the order parameter with local quenched fields.

Heat capacity of nanostructured BaTiO3 ceramics

The temperature dependence of the heat capacity of nanostructured BaTiO3 ceramics produced by the solid-phase method has been studied; before sintering, the synthesized charge is subjected to a severe action in Bridgman anvils in combination with shear deformation. It has been found that the ferroelectric transition is substantially smeared and the phase transition temperature decreases nonlinearly with increasing applied pressure. It has been shown that the defect structure plays a dominant role in the formation of physical properties of the ceramics.

X-Ray, Optical and Dielectric Studies of Diffused Phase Transitions in NaNbO3-Based Solid Solution Crystals

In flux-grown (1−x)NaNbO3-(x)Gd1/3NbO3 solid solution crystals a diffusion of the dielectric permittivity ϵ maximum grows with x and increases dramatically when x exceeds a threshold value x0 ≈ 0.1. Optical studies by the rotating-polarizer method show that Gd-doping results in a very small mean size of twins and the distribution of the birefringence image becomes very messy. In the x < x0 range the changes of lattice parameters and birefringence corresponding to the ϵ(T) anomaly were revealed. The results obtained are in line with the assumption that phase transition diffusion in NaNbO3 is a result of the local strains stemmed from the impurities.

Phase transitions, magnetic and dielectric properties of PbFe0.5Nb0.5O3

ABSTRACT In this paper the investigation of relaxor ferroelectric PbFe0.5Nb0.5O3 has been carried out using the method of X-ray diffraction, magnetic and dielectric measurements over a wide range of temperatures and frequencies. It has been shown that in single crystals there is high-temperature phase transition from the ferroelectric phase to the cubic phase at a temperature of 367 K. The anomalies detected in the dependences of magnetic susceptibility χ (T) and the magnetic moment m (T) in polycrystalline at room temperature and above were found to be correlating with the anomalies detected by structural, EPR spectroscopic and dielectric measurements.

Nanostructured multiferroic PbFe0.5Nb0.5O3 and its physical properties

Polycrystalline multiferroic PbFe0.5Nb0.5O3 (PFN) fabricated by a solid-phase method is studied. Before sintering, a synthesized PFN powder is processed in Bridgman anvils via a force action in combination with shear deformation (FASD) at room temperature. The electrophysical properties and structural parameters of processed samples and a reference sample are compared. Point defects are shown to play a key role in the formation of the physical properties beginning from an FASD of 200 MPa.

Properties of the ferroelectric ceramics PbSc0.5Ta0.5O3 fabricated from an ultradispersed powder

The relaxor ceramics PbSc0.5Ta0.5O3 produced from an ultradispersed powder is studied by X-ray diffraction and dielectric measurements. Before sintering, the powder was subjected to treatment in Bridgman anvils in combination with shear deformation. This method is shown to affect the order parameter and dielectric properties of the ceramics without using long-term high-temperature annealing.

Controlling the physical properties of PbIn0.5Nb0.5O3 ferroelectric ceramics by intense mechanical action with shear

PbIn0.5Nb0.5O3 (PIN) ferroelectric relaxer ceramics obtained by the solid-phase method is studied. Prior to sintering, the synthesized charge is subjected to mechanical action in Bridgman anvils at room temperature. The electrophysical properties of the reference sample and test samples are compared. It is concluded that mechanical treatment of the material at the stage of preparation allows one to control the physical properties of ferroelectric ceramics. Starting from a certain amount of the action, the electrophysical properties of PIN ceramics vary nonmonotonically.

Gd3+-Doped Magnetic Nanoparticles for Biomedical Applications

Magnetic nanoparticles (MNPs) made of iron oxides with cubic symmetry (Fe3O4, γ-Fe2O3) are demanded objects for multipurpose in biomedical applications as contrast agents for magnetic resonance imaging, magnetically driven carriers for drug delivery, and heaters in hyperthermia cancer treatment. An optimum balance between the right particle size and good magnetic response can be reached by a selection of a synthesis method and by doping with rare earth elements. Here, we present a microwave-assisted polyol synthesis of iron oxide MNPs with actual gadolinium (III) doping from 0.5 to 5.1 mol.%. The resulting MNPs have an average size of 14 nm with narrow size distribution. Their surface was covered by a glycol layer, which prevents aggregation and improves biocompatibility. The magnetic hyperthermia test was performed on 1 and 2 mg/ml aqueous colloidal solutions of MNPs and demonstrated their ability to rise the temperature by 3°C during a 20–30 min run. Therefore, the obtained Gd3+ MNPs are the promising material for biomedicine.

Mechanical activation and physical properties of Pb(Zr0.56Ti0.44)O3

ABSTRACT The Pb(Zr0.56Ti0.44)O3 (PZT) ceramics was subjected to a pressure-induced activation at 320 MPa in a Bridgman anvil, where a load pressure was combined with a shear deformation. The induced changes in the linear and angular parameters of a unit cell, in the ratio of coexisting rhombohedral (R3m) and tetragonal (P4mm) phases as well as in the dielectric properties were analyzed.

Nanostructured SmFeO3 electrophysical properties

Samarium orthoferrite conventional and nanostructured ceramic physical properties and structure investigations are reported in the paper. Ceramic samples have been prepared both by classical sintering method after solid phase synthesis and by Bridgman anvil mechanoactivation after synthesis. The authors have established that the mechanoactivation suppress direct current conductivity and increase spontaneous polarization. Polycrystalline samarium orthoferrite physical properties can be purposefully varied on fabrication stage without doping.