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Calculations have been conducted to show that it may be feasible to enhance the tetragonality ( c / a ratio) of tetrataenite ( L 1 0 ; P 4 / m m m ) by charging it with hydrogen, a process that can be achieved at ambient temperature, well below the ordering temperature of the FeNi compound. Although the saturation magnetisation is slightly compromised, the magnetocrystalline anisotropy should increase significantly. It is now worth doing experiments to establish or disprove the results, because the energy of inserting a single hydrogen atom into the location that enhances tetragonality is slightly greater than that in a sub-optimal site in the context of increasing the c / a ratio. Changes in tetragonality as a function of the location of the hydrogen atom can be explained in terms of the relative strengths of the Fe-H and Ni-H bonds. [ABSTRACT FROM AUTHOR]

This study successfully synthesized high-tetragonality barium titanate (BaTiO3) particles with a small particle size by implementing ball milling in the solid-state synthesis of BaTiO3 and utilizing nanoscale raw materials. This study also addressed the issues of impurities and uneven particle size distribution that could exist in the synthesized BaTiO3 particles. The crystal structure, morphology, and particle size of the synthesized BaTiO3 particles have been meticulously analyzed and discussed through the use of techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and the laser particle size analyzer. BaTiO3 has been successfully synthesized, exhibiting a uniform particle size with an average diameter of 170 nm and a high tetragonality value of 1.01022. This new solid-state synthesis method provided insights to avoid the impact of "size effects" during the process of electronic device miniaturization. [ABSTRACT FROM AUTHOR]

Tetragonal barium titanate was synthesized from barium hydroxide octahydrate and titanium tetrachloride through a simple one-step hydrothermal method. The effect of different solvents on the crystal structure and morphology of barium titanate nanoparticles during the hydrothermal process was investigated. Except for ethylene glycol/water solvent, impurity-free barium titanate was synthesized in pure water, methanol/water, ethanol/water, and isopropyl alcohol/water mixed solvents. Compared with other alcohols, ethanol promotes the formation of a tetragonal structure. In addition, characterization studies confirm that particles synthesized in methanol/water, ethanol/water, and isopropyl alcohol/water mixed solvents are smaller in size than those synthesized in pure water. In the case of alcohol-containing solvents, the particle size decreases in the order of isopropanol, ethanol, and methanol. Among all the media used in this study, ethanol/water is considered the optimum reaction media for barium titanate with high tetragonality (defined as the ratio of two lattice parameters c and a, c/a = 1.0088) and small average particle size (82 nm), which indicates its great application potential in multilayer ceramic capacitors. [ABSTRACT FROM AUTHOR]

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This work evaluates the effects of grain growth and tetragonality of the t-ZrO2 phase on the mechanical properties of 3Y-TZP ceramics. Samples were sintered at 1475 °C for 2 h, and at 1600 °C for 2, 12, or 24 h. After sintering, the tetragonal ZrO2 polytypes t and t′ were observed under all sintering conditions, while a residual content of monoclinic ZrO2 was detected in samples sintered at 1600 °C for 24 h. The average grain size was found to vary from 0.65 ± 0.10 to 2.20 ± 0.35 μm. Moreover, zirconia ceramics sintered at 1475 °C for 2 h exhibit higher flexural strength (1210 ± 85 MPa), while samples sintered at 1600 °C for 24 h exhibit the lowest flexural strength (910 ± 90 MPa). These results were related to the progressive formation of Y3+-rich grains (t′-ZrO2) due to the grain boundary segregation-induced phase (GBSIPT) mechanism. Due to the high stabilizer concentration in the solid solution, these grains present lower tetragonality, being highly stable at room temperature. Consequently, the observed strength reduction of samples sintered at 1600 °C for 24 h is related to the presence of the t′-ZrO2 phase, which is less prompt to the phase transformation toughening process, limiting shielding zones’ effectiveness at the crack tip.

Ultrafine ceramic powders with high tetragonality are essential for next-generation multi-layer ceramic capacitors (MLCC). The solid-state reaction synthesis commonly used in industry is challenging to prepare ultra-fine BaTiO 3 powders due to issues of the coarse crystallization at high temperature calcinations. In this study, a two-step calcination combining with the rotary furnace was innovatively used to synthesize ultra-fine BaTiO 3 powders with uniform particle and high tetragonality. Through the reaction kinetics study, it was found that the rotary furnace increases the point contact area of Ba2+ and Ti4+ by improving the heat transfer efficiency of the solid-phase reaction and decreases the diffusion rate of both, so that the diffusion-nucleation-growth rate is greater than the decomposition rate of BaCO 3 to improve the tetragonality of BaTiO 3 powders. The optimal process parameters were determined and the reaction mechanism was studied. Particularly, the optimized two-step assisted rotary furnace calcination had succeeded in preparing finer powders with an average particle size of 250 nm and tetragonality (c / a) of 1.0096. The BaTiO 3 ultrafine powders sintered at 1200 °C has a ceramic density of 96%, dielectric constant of 9173 at the Curie temperature point (131 °C) and a grain activation energy of 0.821 eV, representing excellent dielectric properties and reliability. [ABSTRACT FROM AUTHOR]

This work evaluates the effects of grain growth and tetragonality of the t-ZrO2 phase on the mechanical properties of 3Y-TZP ceramics. Samples were sintered at 1475 °C for 2 h, and at 1600 °C for 2, 12, or 24 h. After sintering, the tetragonal ZrO2 polytypes t and t′ were observed under all sintering conditions, while a residual content of monoclinic ZrO2 was detected in samples sintered at 1600 °C for 24 h. The average grain size was found to vary from 0.65 ± 0.10 to 2.20 ± 0.35 μm. Moreover, zirconia ceramics sintered at 1475 °C for 2 h exhibit higher flexural strength (1210 ± 85 MPa), while samples sintered at 1600 °C for 24 h exhibit the lowest flexural strength (910 ± 90 MPa). These results were related to the progressive formation of Y3+-rich grains (t′-ZrO2) due to the grain boundary segregation-induced phase (GBSIPT) mechanism. Due to the high stabilizer concentration in the solid solution, these grains present lower tetragonality, being highly stable at room temperature. Consequently, the observed strength reduction of samples sintered at 1600 °C for 24 h is related to the presence of the t′-ZrO2 phase, which is less prompt to the phase transformation toughening process, limiting shielding zones' effectiveness at the crack tip. [ABSTRACT FROM AUTHOR]

The results of the previous investigations of martensite crystal structure in the carbon steels, in which, based on the doublet splitting of some XRD lines, the conclusion on tetragonality of martensite was made, is analysed. As proposed, the crystal structure of martensite in the carbon steels is considered as a system of the lattice blocks with C atoms at the block axes and the distorted lattices without carbon atoms around the blocks. Carbon concentration in the steel specifies quantity of the blocks. Edges of the lattices in the blocks and outside them have different sizes depending on the distance to the block axis with carbon atom. As defined, the martensite crystal structure in the carbon steels is pseudotetragonal or trigonal. New approach is proposed for an explanation of a great width value of the martensite XRD lines in the carbon steels. [ABSTRACT FROM AUTHOR]

A crucial step in the preparation of yttria-stabilized zirconia materials (YSZ) is the final sintering step. Sintering parameters affect phase composition, grain growth and porosity of the material which, in turn, influence both mechanical and optical properties. Discrepancies of + /- 5% are common between actual and displayed firing temperatures depending on sintering furnace brand and condition. The aim of this study was therefore to investigate how such sintering temperature deviations in dental furnaces compared to the recommended firing protocols affected certain material properties of different yttria-stabilized zirconia materials. Disc-shaped specimens were made from four different translucent and high translucent YSZ-powders and analysed regarding crystal structure; unit cell volume for the c, t, and t' -phases along with the tetragonality for the t and t' phases. Biaxial flexure strength and the spectral transmittance through the ceramic specimens were also measured. Deviations of 5% from the sintering temperature recommended for YSZ materials with different yttria content influenced material properties such as light transmittance, flexural strength, crystal phase fractions, tetragonality, and grain growth. Too low temperature resulted in decreased strength for some of the translucent zirconia materials, while others where less affected. Light transmittance varied depending on several factors such as grain size, crystal phase fractions and binder content in the start material prior to pre-sintering. The use of high quality, wellcalibrated furnaces is crucial when sintering YSZ materials to avoid unwanted material changes. Deviations of 5% from the sintering temperature recommended for YSZ materials with different yttria content influence material properties such as light transmittance, flexural strength, crystal phase fractions, tetragonality, and grain growth. Too low temperature results in decreased strength for some translucent zirconia materials, while others are less affected. Light transmittance varies depending on several factors such as grain size, crystal phase fractions and binder content in the start material prior to pre-sintering. Consequently, the use of high quality, well-calibrated furnaces is crucial when sintering YSZ materials to avoid unwanted material changes. [ABSTRACT FROM AUTHOR]

A study is made of relationships between composition, processing, structure and properties of biphasic zirconia bioceramics. The focus is on zirconia compositions with different yttria dopant contents used in modern dental restorations, namely 3–5 mol% yttria stabilized zirconia (3YSZ, 4YSZ, and 5YSZ). Crystallographies and densities are surveyed, sintering conditions examined, and microstructures characterized. Strength and optical tests are conducted on each YSZ, and dependencies on sintering temperature, cubic content and grain size analyzed. Strength correlates with the amount of tetragonal zirconia (t -ZrO 2) crystals with large lattice distortions (tetragonality). YSZ translucency correlates with content of cubic zirconia (c -ZrO 2) and t -ZrO 2 with low levels of tetragonality. Consistent with literature reporting, the materials rank in decreasing order 3YSZ, 4YSZ to 5YSZ for strength but increasing order for translucency. However, for a given composition, the data suggest that the strengths of densely sintered 3YSZ and 4YSZ actually increase with translucency, although that of 5YSZ remains undiminished. These trends are in apparent contradiction to prevailing experience, and offer potential future processing routes to optimization of clinical materials. [ABSTRACT FROM AUTHOR]

For decades, improving the piezoelectric properties of piezoelectric materials is one of the key research directions. In this paper, a novel co-doping acceptor-donor (Li+-Sm3+) method is proposed to enhance the piezoelectric properties of PbZr 0.52 Ti 0.48 O 3 (PZT) ceramics. Compared with our previous works, the difference are that Li+-Al3+ or Li + -La3+ ionic pairs occupy sites along the [001] direction while Li+-Sm3+ tends to replace Pb2+ parallels to the [100] direction. 1.5 mol% Li+-Sm3+ enhances the tetragonality of PZT, the maximum polarization intensity, residual polarization intensity and relative coercive field are enhanced. Li+-Sm3+ (1.5 mol%) enhanced the d 33 of PZT from 150 to 405 pC/N, the field to strain exceeds 0.16%. The results show that the piezoelectric enhancement mechanism of PZT is mainly due to the tetragonal increase of PZT crystal, the larger spontaneous polarization intensity significantly improves the piezoelectric properties. This work presents a new method to enhances the piezoelectric properties of piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

The literature (experimental and theoretical) data on the tetragonality of martensite with interstitial–substitutional alloying elements and vacancies are reviewed and analysed. Special attention is paid to the studying the martensitic αʺ-Fe16N2-type phase with unique and promising magnetic properties as an alternative to the rare-earth intermetallics or permendur on the world market of the production of permanent magnets. The period since its discovery to the current status of research is covered. A statistical-thermodynamic model of ‘hybrid’ interstitial–substitutional solid solution based on a b.c.t. crystal lattice, where the alloying non-metal constituents (impurity atoms) can occupy both interstices and vacant sites of the host b.c.c.(t.)-lattice, is elaborated. The discrete (atomic-crystalline) lattice structure, the anisotropy of elasticity, and the ‘blocking’ and strain-induced (including ‘size’) effects in the interatomic interactions are taken into account. The model is adapted for the non-stoichiometric phase of Fe–N martensite maximally ordered by analogy with αʺ-Fe16N2, where nitrogen atoms are in the interstices and at the sites of b.c.t. iron above the Curie point. It is stressed an importance of adequate data on the available (in the literature) temperature- and concentration-dependent microscopic energy parameters of the interactions of atoms and vacancies. The features of varying (viz. non-monotonic decreasing with increasing temperature) the relative concentration of N atoms in the octahedral interstices of b.c.t. Fe, and therefore, the degree of its tetragonality (correlating with this concentration) are elucidated. Within the wide range of varying the total content of introduced N atoms, the ratio of the equilibrium concentration of residual site vacancies to the concentration of thermally activated vacancies in a pure b.c.c. Fe is demonstrated at a fixed temperature.

Tetragonality occurs as a result of stretching the crystal structural lattice of perovskite along one of its lattice vectors such that the three axes are mutually perpendicular with two of the axes having equal lengths. This tetragonality distortion easily triggers functional properties such as pyroelectricity, ferroelectricity, capacitance and piezoelectricity among others, while synthesizing functional ceramics for a particular application. This work addresses and circumvents the challenges of experimental stress involved in functional ceramics synthesis by developing Newtonian search based support vector regression (GSB-SVR) model for perovskite tetragonality prediction using dopants concentration and ionic radii as the model predictors. The performance of proposed GSB-SVR model is compared with the existing method and better performance is obtained. The influence of lanthanides and zirconium incorporation on functional ceramics on the material tetragonality is also modeled by the developed GSB-SVR model. The precision of the developed model, its easily fetched predictors and pre-laboratory ability to effectively and efficiently model the perovskite tetragonality are of high importance in tailoring and enhancing functional properties of materials for desired applications.

Tetragonality occurs as a result of stretching the crystal structural lattice of perovskite along one of its lattice vectors such that the three axes are mutually perpendicular with two of the axes having equal lengths. This tetragonality distortion easily triggers functional properties such as pyroelectricity, ferroelectricity, capacitance, and piezoelectricity among others, while synthesizing functional ceramics for a particular application. This work addresses and circumvents the challenges of experimental stress involved in functional ceramics synthesis by developing a Newtonian search-based support vector regression (GSB-SVR) model for perovskite tetragonality prediction using dopants concentration and ionic radii as the model predictors. The performance of the proposed GSB-SVR model is compared with the existing Kelvin & Rick model and better performance of 35.82% improvement based on mean absolute percentage error (MAPE) and 36.44% improvement based on mean absolute error (MAE) is obtained. The influence of lanthanides and zirconium incorporation on functional ceramics on the material tetragonality is also modeled by the developed GSB-SVR model. The metal in the lanthanide series considered includes lanthanum (La), praseodymium (Pr), Neodymium (Nd), and samarium (Sm). The obtained variation in their tetragonality follows the same trend as their variation in atomic numbers. Maximum distortion occurs between concentrations of 0.05 and 0.1, and each of the examined tetragonality distortions has a parabolic tetragonality distortion variation. Titanium and zirconium dopants were incorporated into the crystal lattice structure of Pb0:9Ba0:1(ZrxTi1-x)O3 and Pb0:9Ba0:1(Zrx-1Tix)O3. The tetragonality distortion in Pb0:9Ba0:1(ZrxTi1-x)O3 was observed to be minimum while Pb0:9Ba0:1(Zrx-1Tix)O3 perovskite show maximum tetragonality distortion. The observed tetragonality distortion can be utilized to enhance the functional properties of perovskite. The precision of the developed model, its easily fetched predictors, and its pre-laboratory ability to effectively and efficiently model the perovskite tetragonality are of high importance in tailoring and enhancing functional properties of materials for desired applications. [ABSTRACT FROM AUTHOR]

A comparative study is reported on the ferroelectric ceramics with compostional formula Ba 0 · 98 La 0 · 02 Ti 0 · 98 Fe 0 · 02 O 3 (BLTF1) and Ba 0 · 97 La 0 · 02 Ti 0 · 98 Fe 0 · 02 O 3 (BLTF2; valency compensated). The samples were prepared by solid state route and sintered in air at 1325 °C for 4 h. The X-ray diffraction analysis confirmed the formation of tetragonal perovskite phase. The prepared samples were characterized for their dielectric and ferroelectric properties at different temperatures at 1, 5, 10 and 100 kHz. Enhancement in ferroelectric properties (P r = 11.25 μC/cm2, E c = 9.05 kV/cm) was observed in BLTF2 ceramics as compared to BLTF1 ceramics (P r = 6.53 μC/cm2, E c = 9.35 kV/cm) along with the observation of electrocaloric effect. The value of piezoelectric coefficient 'd 33 ' was found to be 140 pC/N and 163 pC/N for BLTF1 and BLTF2 samples respectively. The present investigations show that the valency compensation method can improve the ferroelectric properties of the ferroelectric ceramics thereby making them more suitable for different applications. [ABSTRACT FROM AUTHOR]

Zirconia-alumina composites couple the high toughness of zirconia with the peculiar properties of alumina, i.e., hardness, wear, and chemical resistance, so they are considered promising materials for orthopedic and dental implants. The design of high performance zirconia composites needs to consider different aspects, such as the type and amount of stabilizer and the sintering process, that affect the mechanics of toughening and, hence, the mechanical properties. In this study, several stabilizers (Y2O3, CuO, Ta2O5, and CeO2) were tested together with different sintering processes to analyze the in situ toughening mechanism induced by the tetragonal-monoclinic (t-m) transformation of zirconia. One of the most important outcomes is the comprehension of the opposite effect played by the grain size and the tetragonality of the zirconia lattice on mechanical properties, such as fracture toughness and bending strength. These results allow for the design of materials with customized properties and open new perspectives for the development of high-performance zirconia composites for orthopedic implants with high hydrothermal resistance. Moreover, a near-net shape forming process based on the additive manufacturing technology of digital light processing (DLP) was also studied to produce ceramic dental implants with a new type of resin-ceramic powder mixture. This represents a new frontier in the development of zirconia composites thanks to the possibility to obtain a customized component with limited consumption of material and reduced machining costs. [ABSTRACT FROM AUTHOR]

Conventionally, tetragonality in BaTiO 3 powder is attributed to grain size, disregarding the role of Ba/Ti ratio. However, our study reveals a significant impact of Ba/Ti ratio on tetragonality in BaTiO 3. With an increase in Ba/Ti ratio from 0.990 to 1.010, particle size remains around 200 nm. Tetragonality initially rises from 1.006 to a maximum of 1.0092 at Ba/Ti = 1.000, then decreases to 1.005. Lower tetragonality is associated with Ba or Ti vacancies, using density functional theory (DFT), we analyzed the electron density and lattice distinction in BaTiO 3 powders. Both Ba and Ti vacancies affect lattice distortion, the Ti vacancies leading to more significant lattice expansion and lower tetragonality than Ba vacancies. Using this powder, we fabricated high-density BaTiO 3 ceramics and multi-layer ceramics capacitors (MLCCs) with X7R temperature stability (−55 to 125 °C, ±15% coefficient) and excellent reliability. This strategy has broad implications for tetragonal BaTiO 3 nanopowders and MLCCs development. [Display omitted] • The detailed observation and description of Ba or Ti vacancies in BaTiO 3. • The effects of vacancies on tetragonality were calculated by first principles. • The vacancies in BaTiO 3 cause lattice distortion and reduced tetragonality. • Ba vacancies have less impact on tetragonality and degradation performance than Ti. [ABSTRACT FROM AUTHOR]

The crystal structure of martensite in carbon steels is proposed to consider as a defined system of the lattices blocks. Each block consists of four lattices with carbon atom at the central axis of the block. There are lattices without carbon atoms in steels. Carbon concentration in steel determines the quantity of the blocks with C atom. Edges of the lattices in the blocks and outside them have different sizes that depend on the distance to the block axis with carbon atom. It is necessary to consider the martensitic crystal structure in the carbon steels as pseudotetragonal or pseudocubic. Reasons of the large width of the XRD lines of the martensitic phase in the carbon steels are considered and their explanation is proposed. The number of the c edges, which are changed in the same way, determines the diffraction lines width of the martensite in the carbon steels. [ABSTRACT FROM AUTHOR]

Electron Backscatter Diffraction (EBSD) is a widely used approach for characterising the microstructure of various materials. However, it is difficult to accurately distinguish similar (body centred cubic and body centred tetragonal, with small tetragonality) phases in steels using standard EBSD software. One method to tackle the problem of phase distinction is to measure the tetragonality of the phases, which can be done using simulated patterns and cross‐correlation techniques to detect distortion away from a perfectly cubic crystal lattice. However, small errors in the determination of microscope geometry (the so‐called pattern or projection centre) can cause significant errors in tetragonality measurement and lead to erroneous results. This paper utilises a new approach for accurate pattern centre determination via a strain minimisation routine across a large number of grains in dual phase steels. Tetragonality maps are then produced and used to identify phase and estimate local carbon content. The technique is implemented using both kinetically simulated and dynamically simulated patterns to determine their relative accuracy. Tetragonality maps, and subsequent phase maps, based on dynamically simulated patterns in a point‐by‐point and grain average comparison are found to consistently produce more precise and accurate results, with close to 90% accuracy for grain phase identification, when compared with an image‐quality identification method. The error in tetragonality measurements appears to be of the order of 1%, thus producing a commensurate ∼0.2% error in carbon content estimation. Such an error makes the technique unsuitable for estimation of total carbon content of most commercial steels, which often have carbon levels below 0.1%. However, even in the DP steel for this study (0.1 wt.% carbon) it can be used to map carbon in regions with higher accumulation (such as in martensite with nonhomogeneous carbon content). Lay Description: Electron Backscatter Diffraction (EBSD) is a widely used approach for characterising the microstructure of various materials. However, it is difficult to accurately distinguish similar (BCC and BCT) phases in steels using standard EBSD software due to the small difference in crystal structure. One method to tackle the problem of phase distinction is to measure the tetragonality, or apparent 'strain' in the crystal lattice, of the phases. This can be done by comparing experimental EBSD patterns with simulated patterns via cross‐correlation techniques, to detect distortion away from a perfectly cubic crystal lattice. However, small errors in the determination of microscope geometry (the so‐called pattern or projection centre) can cause significant errors in tetragonality measurement and lead to erroneous results. This paper utilises a new approach for accurate pattern centre determination via a strain minimisation routine across a large number of grains in dual phase steels. Tetragonality maps are then produced and used to identify phase and estimate local carbon content. The technique is implemented using both simple kinetically simulated and more complex dynamically simulated patterns to determine their relative accuracy. Tetragonality maps, and subsequent phase maps, based on dynamically simulated patterns in a point‐by‐point and grain average comparison are found to consistently produce more precise and accurate results, with close to 90% accuracy for grain phase identification, when compared with an image‐quality identification method. The error in tetragonality measurements appears to be of the order of 1%, thus producing a commensurate error in carbon content estimation. Such an error makes an estimate of total carbon content particularly unsuitable for low carbon steels; although maps of local carbon content may still be revealing. Application of the method developed in this paper will lead to better understanding of the complex microstructures of steels, and the potential to design microstructures that deliver higher strength and ductility for common applications, such as vehicle components. [ABSTRACT FROM AUTHOR]

To find out the main features of symmetry-energy and structural-entropy aspects of interaction of impurity and solvent, a configuration model for the diffusionless formation of 'hybrid' interstitial-substitutional solid solution Me-X, where the interacting non-metal (X) atoms may occupy both octahedral interstices and sites of the b.c.c.(t.) metal (Me) lattice with vacancies, is developed. The discrete (atomic-crystalline) lattice structure, the anisotropy of elasticity, strain-induced ('size', etc.) as well as 'blocking' effects in the interatomic interactions are taken into account. An example of the simplest alloy isostructural to the nonstoichiometric Fe-N-martensite with a maximal α″-Fe16N2-type long-range order, but with X atoms in the octahedral interstices and sites of the b.c.t.-Me, is considered. An adequate set of the temperature- and concentration-dependent interatomic-interaction-energy parameters in such a solution is used to answer the following two questions. (i) Which are the features of varying the relative concentration of X atoms in the octahedral interstices of the b.c.t.-Me and, thus, its tetragonality degree, when the temperature increases? (ii) How can the equilibrium concentration of residual vacancies at the sites (in a wide range of changing the total content of introduced X atoms) correlate with the concentration of thermally activated vacancies in the impurity-free b.c.c.-Me at a fixed temperature?. [ABSTRACT FROM AUTHOR]

From the standpoint of the method of phase diagrams of martensitic transformations (PDMF), an analysis of the literature data, obtained experimentally and theoretically in the study of martensitic transformations in carbon steels, is performed starting from the 20s of the last century and ending with modern works. In accordance with the PDMF, it is impossible to consider polymorphic phase transformations (including martensitic ones) without taking into account the participation of vacancies in them. Just vacancies are the connecting link that unites volume, deformations, and stresses into a single whole. A comparison of the known data on the changes in the crystal lattice parameters of austenite, ferrite, and martensite allow us to conclude that, during the formation of a martensitic crystal, carbon simply shifts in all cells along the edge of the quenching stress that is favourably oriented relative to the current gradient. In this case, the tetragonality of martensite in carbon steels is determined not by carbon, but by vacancy-carbon complexes, which arise as a result of, for example, quenching. A scheme for determining the waves of concentration inhomogeneities in carbon steels is proposed, which made it possible to construct the dependence of the temperatures of martensitic transformations (Ms and Mf) on the carbon concentration. Based on these constructions, it was shown that martensite cannot contain carbon more than 1% wt. The PDMF method allows dividing the process of martensite formation into two stages. The first stage is the formation of elastic 'austenitic' martensite (γ′-phase) by shear during cooling. The crystal is deformed until the γ′-phase remains stable. The second stage is the loss of stability, the isolation of the crystal and its transformation into a 'ferritic' (α′-phase) martensite. The second stage is a quantum mechanical phenomenon, since the process is caused by a change in interatomic bonds. The process proceeds instantly, with a simply shift and at a constant temperature. [ABSTRACT FROM AUTHOR]

The literature (experimental and theoretical) data on the tetragonality of martensite with interstitial-substitutional alloying elements and vacancies are reviewed and analysed. Special attention is paid to the studying the martensitic α″-Fe16N2-type phase with unique and promising magnetic properties as an alternative to the rareearth intermetallics or permendur on the world market of the production of permanent magnets. The period since its discovery to the current status of research is covered. A statistical-thermodynamic model of 'hybrid' interstitial-substitutional solid solution based on a b.c.t. crystal lattice, where the alloying non-metal constituents (impurity atoms) can occupy both interstices and vacant sites of the host b.c.c.(t.)-lattice, is elaborated. The discrete (atomic-crystalline) lattice structure, the anisotropy of elasticity, and the 'blocking' and strain-induced (including 'size') effects in the interatomic interactions are taken into account. The model is adapted for the non-stoichiometric phase of Fe-N martensite maximally ordered by analogy with α″-Fe16N2, where nitrogen atoms are in the interstices and at the sites of b.c.t. iron above the Curie point. It is stressed an importance of adequate data on the available (in the literature) temperature- and concentration-dependent micro-scopic energy parameters of the interactions of atoms and vacancies. The features of varying (viz. non-monotonic decreasing with increasing temperature) the relative concentration of N atoms in the octahedral interstices of b.c.t. Fe, and therefore, the degree of its tetragonality (correlating with this concentration) are elucidated. Within the wide range of varying the total content of introduced N atoms, the ratio of the equilibrium concentration of residual site vacancies to the concentration of thermally activated vacancies in a pure b.c.c. Fe is demonstrated at a fixed temperature. [ABSTRACT FROM AUTHOR]

The Raman peaks of metastable yttria‐stabilized zirconia changed with annealing at high temperatures even before the onset of transformation to any monoclinic phase, leading to ambiguous determination of stress‐free references. In this work, the evolution of the Raman bands of metastable YSZ with annealing for different times at different high temperatures were analyzed using the tetragonality variation, which was consequent on the cation redistribution activated by thermal diffusion. The Raman bands linearly varied with the volume weighted tetragonality over the range studied (1.009‐1.015). The cation diffusion changed the bonds length and the associated Raman modes frequencies. A semiempirical equation was established to amend the available calculation for residual stresses by Raman spectroscopy, based on the variation coefficients ratio of two Eg Raman modes (465 cm−1 and 640 cm−1). [ABSTRACT FROM AUTHOR]

Measurements of the local tetragonality in Fe-C martensite at microstructural length-scale through pattern matching of electron backscatter diffraction patterns (EBSPs) and careful calibration of detector geometry are presented. It is found that the local tetragonality varies within the complex microstructure by several per cent at largest and that the scatter in the axial ratio is increased at higher nominal carbon content. At some analysis points the local crystal structure can be regarded as lower symmetry than simple body centred tetragonal. A linear relation between the nominal carbon content and averaged local tetragonality measured by EBSD is also obtained, although the averaged axial ratio is slightly below that obtained from more classical X-ray diffraction measurements. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In order to synthesize of high-dispersion and tetragonal BaTiO3 (BT) nanoparticle, a hydrothermal method is used in a mixture of chloride metal sources and KOH with polyvinylpyrrolidone (PVP). The properties of BT–PVPs prepared by different reaction temperature and time are investigated via XRD, FE-SEM, DLS, FT-IR, and TEM to clarify the changes of the crystal phase, dispersion, and particle structure. The reaction is finished at 230 °C for 24 h and the critical reaction condition for that the crystal phase of the obtained BT particle changed from the cubic to the tetragonal is found to be 190 °C fixed in reaction time 24 h, and 9 h. During reaction the PVP on the BT surface decomposed to different form, and the PVP plays the role of dispersant in aqueous solution. By the hydrothermal condition of 230 °C for 24 h almost monodisperse BT–PVP with sizes of 83 nm and tetragonality (c/a) of 1.0062 were synthesized. The structure of nanoparticle, core (BT)–shell (PVP) was investigated by FT-IR and direct observed by TEM and the mechanism of particle growth and dispersion was discussed.

Despite the fact that scientists have been studying the nature of the mechanism of martensite formation for almost a hundred years, these studies remain, still, relevant. In this paper, the authors present two new results related to the classical question of the role of carbon in martensite formation. If, while dissolving in the lattice, the carbon is located in the center of the octahedral emptiness, then under the influence of stresses caused by quenching or deformation, in martensite it is displaced into one of the pyramids of the constituent octahedra. The fact of the independence of the specific atomic volume of phase mismatch during martensitic transformation of iron from the carbon content was found. This fact indicates that the tetragonality of carbon steels is a function not so much of carbon as vacancies. In the pure iron the "vacancy" tetragonality can vary from 1.03 to 1.06.

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Martensitic transformation B2–L10 in the ordered alloy Ni50Mn50, which occurs at comparatively high temperatures (980–920 K), is discussed with the use of dynamic concepts of the wave control of the threshold deformation. The proximity of the observed orientations of martensite-crystal habits (and of twin boundaries) to the planes of the {110} family makes it possible to use the longitudinal waves along the axes 〈001〉 (in the basis of the initial phase) as the driving factors. It is shown that at temperatures of the onset of the transformation there is a satisfactory correspondence between the calculated and experimental data on the tetragonality of martensite and on the volume effect. The opportunity of different dynamic scenarios of the formation of the final phase is noted, namely, of separate crystals; layered structures, in which the crystals of martensite with the identical orientation relationships alternate with the untransformed regions of austenite; and packets of pairwise-twinned crystals. Examples are given of morpho-types corresponding to these scenarios. [ABSTRACT FROM AUTHOR]

Abstract EPR parameters and the local configurations of the transition metal (TM) ions VO2+ and Cu2+ in BaO-TeO 2 -B 2 O 3 glasses were experimentally evaluated and also theoretically verified. From the recorded X-band EPR spectra the spin-Hamiltonian parameters (SHP) were determined. The optical spectra of vanadium doped glass samples revealed a single absorption band at 596 nm which was assigned to 2B 2g → 2B 1g transition, whereas copper doped glasses revealed two absorption bands around 818 and 602 nm which were assigned to 2B 1g → 2B 2g and 2B 1g → 2E 2g transitions respectively. Theoretical studies were accomplished on the EPR and optical factors from perturbation theory. It was observed from both the experimental and theoretical SHP values of vanadium containing glasses that the VO2+ ions are in tetragonally compressed octahedral sites with d xy (2B 2g) ground state, while the copper containing glasses found to be in tetragonally elongated octahedral sites with d x 2 − y 2 (2B 1g) as the ground state. It is found that the magnitude of the relative tetragonal compression ratio (φ) of vanadium ion is less than the relative tetragonal elongation ratio (τ) of copper ion. The nature of the bonding between TM ions (i.e. vanadium and copper) and their ligands was assessed. Theoretical and experimental EPR parameters are in great concurrence with each other. Graphical abstract Local structures of the VO2+ and Cu2+ ion complexes in BTB glasses. Image 1 Highlights • Experimentally evaluated SHP values theoretically verified. • Theoretical studies were carried out from perturbation theory. • The nature of bonding between TM ions and their ligand was assessed. • The relative tetragonal distortion ratio of VO2+ ion is less than Cu2+ ion. [ABSTRACT FROM AUTHOR]

Abstract We present the study of structural, morphological, dielectric, transport and ferroelectric properties of (1- x)BFO– x PTO solid solutions, with 0.3 ≤ x ≤ 0.6, prepared via non-conventional synthesis methods. These methods include Sol-gel and Single-step solid state method. Structural analysis revealed presence of mixed phases i.e. monoclinic (CC) and tetragonal (P4mm) phases, for all compositions showing a Morphotropic Phase Boundary. For the compositions with higher concentration of PTO, an increase in tetragonal phase fraction has been observed. Quantitative analysis showed, in general, higher value of c / a (i.e. tetragonality) for all samples as compared to the bulk PTO. The morphological analysis shows small grain size irrespective of synthesis method and composition. The low temperature frequency dependent tangent loss shows dielectric relaxation with small magnitude of dielectric constant indicating absence of extrinsic contributions. High temperature dielectric anomaly is observed around 400–500 K corresponding to magnetic phase transformation of BFO at Neel temperature which suggest the presence of magneto-electric coupling in specific compositions. Sol-gel prepared composite appeared to be more resistive than the Single-step synthesized composite and shows Arrhenius type dependence of high temperature ac conductivity. Ferroelectricity was observed in all ceramic samples which sustained high applied electric field up to 190 kV/cm. Finally, a correlation between polarization, tetragonal phase fraction and c/a ratio, has been drawn and discussed. It is concluded that c/a ratio (i.e. tetragonality) is more important parameter which can be tuned to achieve enhanced ferroelectric response as compared to the tetragonal phase fraction in (1- x)BFO– x PTO solid solutions. Graphical abstract Image 1 Highlights • Synthesis of BiFeO 3 - x PbTiO 3 solid solutions through non-conventional method. • Rietveld analysis revealed presence of MPB in all solid solutions. • Dielectric anomaly at magnetic phase transition reveals magneto-electric coupling. • Between polarization, tetragonal phase fraction and c/a ratio correlation is drawn. • c/a ratio (tetragonality) is found to effect ferroelectric response. [ABSTRACT FROM AUTHOR]

In this work, solid solutions of (0.88–x)Bi 0.5 Na 0.5 TiO 3 –0.12BaTiO 3 – xBa(Ti 0.5 Ni 0.5 )O 3–δ were designed and prepared. These compositions exhibit ferroelectricity at room temperature, with the tetragonal symmetry. The c/a values are varied from ∼1.0067 (x = 0.1) to ∼1.0208 (x = 0.04). A transition from the high–temperature relaxor state to the low–temperature ferroelectric state is demonstrated by the temperature dependence of dielectric data and Raman spectrum. The direct bandgap decreases from 3.40 eV for x = 0 to 3.16 eV for x = 0.1. The Ba(Ti 0.5 Ni 0.5 )O 3–δ addition leads an additional optical absorption peak in the visible range. The obvious photodielectric effect was discovered. In particular, the relative permittivity of the x = 0.1 composition rises from ∼756 to ∼807 under light illumination. [ABSTRACT FROM AUTHOR]

Abstract: By‐products including unwanted phase formation and/or unreacted starting materials are normally seen in the outcome of solid‐state synthesis approaches used in the literature for powder processing of advanced materials; this drawback requires critical attention and must be addressed in the new synthesis pathways in order to obtain quality powder products. A high energy mechanical milling approach was developed in this work. Addressing the drawback, the starting materials were mechanically activated by a high energy ball mill before their mixing step. It was found that highly pure barium titanate nanopowders with high tetragonality character are obtained using the approach developed here. The work also characterized tetragonality, role of the mechanical activation and postmilling thermal treatment on structure, phase formation and morphology of the obtained powder products. It was found that the mechanical activation accelerates the kinetic of formation of barium titanate and enhances the purity and tetragonality of the final products. The mechanism behind this achievement and the related reaction pattern are disclosed in this work. In order to obtain highly pure tetragonal barium titanate, a calcination temperature of 1173 K (900°C) after 30 hours mechanical activation is necessary; if these requirements are not satisfied, the final powder product contains impure phases and/or unreacted starting materials. The results also indicated that the processing conditions result in enhancement of tetragonality character of the final powder products. It seems that the method developed here can be used as a generalized methodology for obtaining the quality highly pure monosized nanocrystals of the mixed oxides for assembling in nanotechnology. [ABSTRACT FROM AUTHOR]

Abstract (0.75-x)BiFeO 3 -0.25PbTiO 3 -xBa(Zr 0.25 Ti 0.75)O 3 (BF-PT-BZT) ternary solid solutions were prepared by the solid state reaction method. It was found from X-ray diffraction analysis that the morphotropic phase boundary (MPB) between tetragonal(T) and rhombohedral(R) phases occurred at the composition range of x from 0.13 to 0.28. For BF-PT-base ceramics, the addition of BZT can effectively decreased the tetragonality (c/a) and improved the ferroelectric as well as piezoelectric properties. The maximum value of piezoelectric constant d 33 and electromechanical coupling factor kp were 182 pC/N and 0.34, respectively. Also, the ferroelectric transition temperature (T c) of BF-PT-BZT ceramics varied in the range of 550–298 °C. It is believed that the BF-PT-BZT ternary solid solutions could be a good candidate for high-temperature applications. [ABSTRACT FROM AUTHOR]

The Dielectric, Electric Properties and Microstructure of Ba Mnx Ti1-x O3 (where x = 0.0, 0.01, 0.02, 0.03, 0.04) ceramics have been investigated. The ceramic samples were prepared by Solid-State Reaction Method. The SEM microstructure shows grain size decreased from 192.93 nm down to 167.05 nm. Tetragonal structure was found for samples 0.03% and 0.04% Mn-doped BaTiO3 while others showed pseudo-cubic structure. The Dielectric Constant measurements were executed as a function of temperature. Pure and 0.03% Mndoped ceramics showed improved dielectric constant around Curie temperature region. The temperature dependence of electrical resistivity for all samples were noted acquired that the resistivity changes with the addition of Mn+3 ions in the conduction process accordingly, except pure barium titanate i.e, x=0.0. [ABSTRACT FROM AUTHOR]

Though the uniaxial and hydrostatic pressure dependence of T c yield important insight into the superconductivity of YBa 2 Cu 3 O x ( x  ≈ 6.95–7.0), the understanding of the origin of the pressure effect on this system remains lack of a unified model explanation in a quantitative manner. In order to develop a unified model, we performed first-principles calculations for YBa 2 Cu 3 O 7 under pressure to distinguish the core factors including holes concentration and tetragonality and further combined the two factors with the charge-transfer model to determine the T c . The role of tetragonality was identified in determining the uniaxial pressure effect significantly but not as prominent as holes concentration in producing the superconductivity of YBa 2 Cu 3 O x ( x  ≈ 6.95–7.0). The results under pressure from the unified model based on the newly defined tetragonality and holes concentration are in good accordance with that from experiments. With this unified model, we predicted that the better superconductivity in YBa 2 Cu 3 O x ( x  ≈ 6.95–7.0) may appear through 0.025 compression along b axis or 0.025 stretching along a axis. [ABSTRACT FROM AUTHOR]

With supersaturated carbon atoms ordering in the preferential octahedral sites of α-Fe lattice, the martensite formed in medium and high carbon steels exhibit a unique structural feature, tetragonality. In this letter, we reported anomalous nontetragonality of martensite in carbon steels by deforming quenched martensite, indicating that the disordering of interstitial carbon atoms in α-Fe lattice occurs under mechanical deformation. This order-disorder transition of interstitial carbon atoms in carbon steels provides solid experimental evidences of the prediction based on microscopic elasticity theory. [ABSTRACT FROM AUTHOR]

Rapid cooling of the Fe–C fcc solution leads to the formation of a phase called martensite, which has high mechanical properties. It is well known that under stress a martensite has the ability to plastically deform within a small range, despite the large value of the macroscopic yield strength. This effect is explained in different ways, mainly on the basis of dislocation theory. We study the impact of external stress on ordering of interstitial atoms in Fe–C solid solutions and formation of tetrahedral distortion of martensite lattice. Molecular dynamics with embedded atom (EAM) interatomic potential is used. According to the simulations, interstitial carbon atoms migrate under external stress applied along the tetragonality direction from z‐sublattice, and tetrahedral distortion of lattice changes its orientation to other ones when the stress exceeds some critical value. This result enables us to justify a new look at the nature of the martensite plastic deformation. The influence of temperature and carbon content on the critical stress value is investigated. [ABSTRACT FROM AUTHOR]

To visualize the varying tetragonal distortions in high carbon martensitic steels by EBSD, two different approaches have been applied on backscattered Kikuchi diffraction (BKD) patterns. A band-edge refinement technique called Refined Accuracy (RA) (Oxford Instruments) is compared with a technique called Pattern Matching (PM), which optimizes the fit to a simulated BKD signal. RA distinguishes between hypothetical phases of different fixed c / a , while PM determines a best fitting continuous c / a by projective transformation of a master pattern. Both techniques require stored BKD patterns. The sensitivity of the c / a -determination was tested by investigating the microstructure of a ferritic steel with an expected c / a = 1. The influence of the Kikuchi pattern noise on c / a was compared for a single or 40 averaged frames per measuring point, and turned out to be not significant. The application of RA and PM on the martensitic microstructure delivered qualitatively similar maps of c / a. The comparison of RA and PM shows that RA is suitably fast and precise during mapping the martensite c / a ratio in analyses of high carbon martensite, especially for fast initial surveys. As RA leads quantitatively to higher noise in c / a , the PM analysis can be used for higher precision results. • Martensite tetragonality measurements using EBSD were performed • Pattern avg. improves precision without large effect on accuracy determination. • PM was compared to RA giving qualitatively similar results • Quantitatively both techniques provided slightly different results • Refined Accuracy provides approx. 0.005 resolution in the c/a determination [ABSTRACT FROM AUTHOR]

The material series of polycrystalline ferroelectric ceramics with compositional formula (Ba 1-x Sm x )(Ti 1-x Fe x )O 3 (with 0 ≥ x ≥ 0.01 in steps of 0.0025) was prepared by solid-state reaction method. The samples were sintered at 1300 °C (for x = 0) and 1325 °C for (x > 0). The sintered samples were subjected to X-ray diffraction (XRD) analysis and found to have single phase with tetragonal perovskite structure. Average grain size decreases with increase in substituent content. Dielectric behavior was studied as a function of temperature at different frequencies (1, 10,100,1000 kHz). The lattice constant ‘c’, tetragonality‘c/a ratio’ and Curie temperature ‘T c ’ was found to decrease with increase in the substituent content whereas the room temperature dielectric constant increases with substituent content. Large value of temperature coefficient of capacitance ‘T cc ’> 10%/°C near T c was observed for all the samples. [ABSTRACT FROM AUTHOR]

Nanosized barium titanate (BaTiO 3 (BTO)) powders with a pure perovskite phase and high c/a ratio were prepared using a two-step hydrothermal approach followed by removal of hydroxyl groups using organic solvents. No trace of carbonate was observed during the preparation process. The tetragonality of the BTO powder increased with an increase in the hydrothermal process duration on treating the powder at 240 °C with the two-step and one-step processes. The tetragonality increased with a decrease in the hydroxyl group content. The advantages of the two-step process can be ascribed to the two-step nucleation and growth process, and in the second step, BTO particles nucleate directly on the BTO crystallites, resulting in a higher crystallinity and tetragonality (c/a ratio). The new method has the potential to be scaled up for mass production of high-quality BTO nanopowder samples suitable for capacitor and sensor applications. [ABSTRACT FROM AUTHOR]

In order to synthesize of high-dispersion and tetragonal BaTiO3 (BT) nanoparticle, a hydrothermal method is used in a mixture of chloride metal sources and KOH with polyvinylpyrrolidone (PVP). The properties of BT-PVPs prepared by different reaction temperature and time are investigated via XRD, FE-SEM, DLS, FT-IR, and TEM to clarify the changes of the crystal phase, dispersion, and particle structure. The reaction is finished at 230 °C for 24 h and the critical reaction condition for that the crystal phase of the obtained BT particle changed from the cubic to the tetragonal is found to be 190 °C fixed in reaction time 24 h, and 9 h. During reaction the PVP on the BT surface decomposed to different form, and the PVP plays the role of dispersant in aqueous solution. By the hydrothermal condition of 230 °C for 24 h almost monodisperse BT-PVP with sizes of 83 nm and tetragonality (c/a) of 1.0062 were synthesized. The structure of nanoparticle, core (BT)-shell (PVP) was investigated by FT-IR and direct observed by TEM and the mechanism of particle growth and dispersion was discussed. [ABSTRACT FROM AUTHOR]

The bainite transformation in a low-carbon Si-containing steel has been studied in situ by synchrotron X-rays. While the austenite is homogeneous prior to transformation, the carbon distribution becomes nonuniform as bainite plates form. This is because of the different degrees of physical isolation of films and blocks of residual austenite. The method for converting dilatational strain into bainite volume fraction, using lattice strain as a reference, during isothermal transformation was found to overestimate it. The bainitic and martensitic ferrite did not exhibit a tetragonal unit cell due to the low-carbon content of the steel and the high transformation temperature. [ABSTRACT FROM AUTHOR]

Nano CuFe 2− x Cr x O 4 ferrite has been prepared by citrate autocombustion method. The impact of heat treatment and Cr contents on the structural phases and parameters were studied by tracing X-ray diffraction (XRD) patterns. As-prepared samples were found to contain a major cubic CuFe 2 O 4 phase associated with minorities of CuO and tetragonal CuFe 2 O 4 phases. Upon annealing at 600 °C, the content of tetragonal phase increased while CuO phase disappeared. On the other hand, replacing Fe by Cr in the CuFe 2− x Cr x O 4 system reduces the formation of the tetragonal phase. Carrying out Rietveld analysis, the phase percentage and lattice parameters of both phases as well as the crystallite size were correlated with Cr content. Moreover, the change of the inversion occupancy parameter and the degree of tetragonality were studied in detail. Finally, magnetic properties including saturation magnetization and coercive field of the annealed samples, and their dependence on the degree of tetragonality and crystallite size, were elaborated using vibrating sample magnetometry (VSM). [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)