High-pressure torsion (HPT) method currently receives much attention as a severe plastic deformation (SPD) technique mainly because of the reports of Prof. Ruslan Z. Valiev and his co-workers in 1988. They reported the efficiency of the method in creating ultrafine-grained (UFG) structures with predominantly high-angle grain boundaries, which started the new age of nanoSPD materials with novel properties. The HPT method was first introduced by Prof. Percy W. Bridgman in 1935. Bridgman pioneered application of high torsional shearing stress combined with high hydrostatic pressure to many different kinds of materials such as pure elements, metallic materials, glasses, geological materials (rocks and minerals), biological materials, polymers and many different kinds of organic and inorganic compounds. This paper reviews the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarizes their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.

A review on high-pressure torsion (HPT) from 1935 to 1988

NaNbO3 (NN) is generally considered as one of the most promising lead-free antiferroelectric (AFE) perovskite materials with the advantages of low cost, low density and nontoxicity. However, the metastable ferroelectric phase causes a large remanent polarization (Pr) at room temperature, seriously hindering the achievement of excellent energy storage properties. Although via the strategy of lowering the radius of B-site ions and polarizability, a number of AFE NaNbO3-based solid solutions with double polarization–electric field loops are successfully constructed, the hysteresis losses are still too large and the Pr value cannot be reduced to near zero. In this study, Bi(Mg2/3Nb1/3)NbO3 (BMN) was chosen to partially substitute the pure NaNbO3 with the intention of enhancing antiferroelectricity and constructing a local random field simultaneously. These short-range interactions effectively suppress the hysteresis loss and Pr, and slim hysteresis loops were observed in the NN–BMN ceramics. A high charged energy density (3.4 J cm−3) and recoverable energy storage density (2.8 J cm−3) with high efficiency (82%) were achieved under 300 kV cm−1 for NN–0.10BMN. Superior stabilities and underdamped discharge abilities were also achieved for NN–0.15BMN with a slightly smaller recoverable energy storage density (2.4 J cm−3) but even higher efficiency (90%). The results reported here demonstrate great potential of the designed NN–BMN ceramics for high-temperature capacitors.

Excellent comprehensive energy storage properties of novel lead-free NaNbO3-based ceramics for dielectric capacitor applications

Since the positive influences of defects on the performance of electroceramics were discovered, investigations concerning on defects and aliovalent doping routes have grown rapidly in the fields of inorganic chemistry and condensed matter physics. In this article, we summarized the types of defects in electroceramics as well as characterization tools of defects and highlighted the effects of intrinsic and extrinsic defects on the material performances with the emphasis on dielectric, ferroelectric, and piezoelectric properties. We mainly introduced defect related theoretical simulation and experimental results in several typical incipient ferroelectrics, ferroelectrics, and antiferroelectrics. Hence, the influences of defects on the crystal lattice were summed up, and then the main physical mechanisms were highlighted. Particularly, the performance enhancements of aliovalently doped electroceramics were also evaluated and reviewed. Finally, the outlook and challenges were discussed on the basis of their current developments. This article covers not only an overview of the state-of-the-art advances of defects and aliovalent doping routes in electroceramics but also the future prospects that may open another window to tune the electrical performance of electroceramics via intentionally introducing certain defects.

Defects and Aliovalent Doping Engineering in Electroceramics.

Correlation between microstructure parameters and anti-cancer activity of the [Mn0.5Zn0.5](EuxNdxFe2-2x)O4 nanoferrites produced by modified sol-gel and ultrasonic methods

Review on Recent Advancements in Severe Plastic Deformation of Oxides by High‐Pressure Torsion (HPT)

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.

Diffuse phase transition in NaNbO3:Gd single crystals

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.

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

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.

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Gd3+-Doped Magnetic Nanoparticles for Biomedical Applications

The pure-phase BiFeO3 was obtained in one stage by solution combustion synthesis. The influence of the heat treatment process on the phase composition, magnetic, and optical properties was studied. The calcination of the powder led to a decrease in the fraction of the impurity phase from 7 to 1% and an increase in the crystallite size. X-ray diffraction revealed the formation of a pure phase upon heat treatment at 600 °C. The band gap of the samples increases from 1.91 to 2.06 eV with an increase in the crystallite size. M–H loops measured at room temperature showed a strong ferromagnetic character. For the initial powder, Ms was ~ 1.9 emu/g. The dependence of the magnetic properties on the crystallite size has been established.

Size-dependent structural parameters, optical, and magnetic properties of facile synthesized pure-phase BiFeO3

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.

K. G. Abdulvakhidov

Papers

Diffuse phase transition in NaNbO3:Gd single crystals

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

Gd3+-Doped Magnetic Nanoparticles for Biomedical Applications

Size-dependent structural parameters, optical, and magnetic properties of facile synthesized pure-phase BiFeO3

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