Tetragonal Ti Research Articles

Closed-form expressions for computing flexoelectric coefficients in textured polycrystalline dielectrics

The volume average of the constituting properties of a textured polycrystalline aggregate (the Voigt average) provides a simple way to estimate the effective properties of such an aggregate in terms of its crystallographic symmetry, texture symmetry, and the properties of the constituting crystallites. Despite the interest in estimate or characterizing flexoelectric properties, few studies have addressed the problem of finding effective flexoelectric properties from the continuum phases of the constituents. Instead, most of them focus on single-crystals at the atomic level. This study provides, for the first time, closed-form expressions that allow the direct flexoelectric coefficients to be computed for textured polycrystalline dielectrics. Crystallites can belong to any class of cubic symmetry or to the tetragonal TI Laue group, while no restriction is imposed on texture symmetry. These expressions are reduced to very simple ones when cubic crystallites with fiber texture are considered. The proposed formulation provides information on the matrix structure of the homogenized material related to the crystallographic symmetry and texture. We close with some illustrative examples.

Enhanced mechanical and biocompatibility performance of Ti(1-)Ag(x) coatings through intermetallic phase modification

Advanced materials combining superior mechanical and biocompatibility performance are of significant interest to extend the lifetime of biomedical devices. In this work, Ag is alloyed with Ti to investigate the role of emerging Ti Ag intermetallic coatings with high mechanical hardness and exceptional biocompatibility. Thin films of Ti (1- x ) Ag (x) were deposited on 316 L steel and glass substrates using magnetron sputtering and subsequently heat-treated to aid Ti Ag intermetallic development. Mechanical properties were then measured and correlated to microstructural and morphological changes in the Ti Ag films. In the as-grown state, the Ti Ag matrix developed different intermetallic structures which increased the hardness of pure Ti films from 5 to >7 GPa. After heat treatment, a peak hardness of 7.39 GPa and elastic modulus of 105 GPa was achieved for a 43 at.% Ag film due to formation of the tetragonal Ti Ag phase and increase of upper surface oxides which act as dislocation barriers. However, at higher Ag concentrations, heat treatment leads to agglomeration of Ag around grain boundaries and decreases the crystallite size, leading to reduction in hardness to <3 GPa. The Ti rich films also depict better cytotoxicity performance following exposure to the L929 cell line, though excellent cell viability values >98% are observed for the entire Ti Ag range. While leached ion concentrations lower than 100 ppb demonstrate excellent biocompatibility of this Ti Ag alloy system. This work demonstrates the first successful attempt to develop biocompatible Ti Ag thin film coatings with high mechanical hardness with the potential to extend the lifetime of medical implants. • First study on biomechanical performance of Ti (1-x) -Ag (x) intermetallic films. • First report on external heat treatment to develop Ti Ag intermetallic thin films. • Ag addition causes transition to tetragonal Ti Ag structure with enhanced hardness. • Heat treatment leads to improved crystallinity and mechanical performance. • Ti Ag films exhibit excellent biocompatibility before and after heat treatment.

P-type cobaltite oxide spinels enable efficient electrocatalytic oxygen evolution reaction.

Currently, energy-efficient electrocatalytic oxygen evolution from water involves the use of noble metal oxides. Here, we show that highly p-conducting zinc cobaltite spinel Zn1.2Co1.8O3.5 offers an enhanced electrocatalytic activity for oxygen evolution. We refer to previous studies on sputtered Zn–Co spinels with optimized conductivity for implementation as (p-type) transparent conducting oxides. Based on that, we manufacture off-stoichiometric conducting p-spinel catalytic anodes on tetragonal Ti, Au–Ti and hexagonal Al-doped ZnO carriers and report the evolution of O2 at Tafel slopes between 40.5 and 48 mV dec−1 and at overpotentials between 0.35 and 0.43 V (at 10 mA cm−2). The anodic stability, i.e., 50 h of continuous O2 electrolysis in 1 M KOH, suggests that increasing the conductivity is advantageous for electrolysis, particularly for reducing the ohmic losses and ensuring activity across the entire surface. We conclude by pointing out the merits of improving p-doping in Zn–Co spinels by optimized growth on a tetragonal Ti-carrier and their application as dimension-stable 3d-metal anodes.

Systematics and anomalies in formation and crystal structures of RScSb and R3Sc2Sb3 rare earth compounds

• New equiatomic RScSb compounds identified for R = La–Nd, Sm, Gd–Tm, Lu, and Y. • The RScSb compounds crystallize in two different crystal structures. • Lighter R (R = La–Nd, Sm) crystallize with the CeScSi-type (tetragonal tI 12, I 4/ mmm ). • Heavier R (R = Gd–Tm, Lu, Y) adopt the CeFeSi-type (tetragonal tP 6, P 4/ nmm ). • New R 3 Sc 2 Sb 3 phases identified for R = Gd–Tm, Lu, Y; β-Yb 5 Sb 3 -type (orth. oP 32, Pnma ). A systematic study of RScSb (R = rare earth) ternary alloys has been carried out by X-ray diffraction, optical and electron microscopy and microprobe analysis. As a result, the new equiatomic RScSb (R = La–Nd, Sm, Gd–Tm, Lu, Y) compounds have been identified. No formation of equiatomic 1:1:1 phases has been observed for Eu and Yb. It has been found the RScSb compounds crystallize in two different crystal structures. The phases formed by the lighter R (La–Nd, Sm) adopt the CeScSi-type (tetragonal tI 12, I 4/ mmm , an ordered variant of the La 2 Sb-type), while the ones containing the heavier R (R = Gd–Tm, Lu, Y) crystallize with the CeFeSi-type (tetragonal tP 6, P 4/ nmm , an ordered derivative of the Cu 2 Sb-type). The latter phases were expected to be dimorphic, thus suggesting they might be polymorphic having the CeScSi-type as the low-temperature form; however, no proof of this was found in the course of the present study. Besides the equiatomic compounds, the R 3 Sc 2 Sb 3 phases have also been identified. They form from Gd-Tm, Lu, included Y, and crystallize in the β-Yb 5 Sb 3 -type (orthorhombic oP 32, Pnma ). The observed lattice parameters , unit cell volume and volume contraction, for both the series of compounds, decrease on going from La to Lu following the lanthanide contraction trend. First principles calculations pinpoint that the differences in the electronic structure are directly related to the differences in the crystal structures of these compounds.

Growth of isothermally-solidified titanium joints using a multi-component Zr–Ti–Cu–Ni–Be amorphous alloy as a brazing filler

Abstract The growth and microstructure properties of Ti (grade 2) joints brazed by a Zr 41.2 Ti 13.8 Ni 10.0 Cu 12.5 Be 22.5 bulk metallic glass alloy filler have been investigated with regard to the control through isothermal solidification. Two characteristic joints were prepared at different isothermal brazing conditions: an acicular growth structure including a continuous segregation in the central area (at 830 °C for 300 s), and a structure with coarse acicular grains throughout the joint (at 830 °C for 1800 s). The primary phase solidified isothermally was hexagonal α-Ti, and upon subsequent cooling, the secondary α- and γ-phases formed at the intercellular regions through a eutectoid decomposition of β-Ti. The γ-phase was identified as having a phase formula of [Ti,(Zr)] 2 (Cu,Ni) with a tetragonal Ti 2 Cu structure ( a = 2.955 A, c = 10.827 A, space group = I 4/mmm). This phase was grown on primary α-Ti grains with an orientation relationship of 10 1 ¯ 0 α ∥ (200) γ and 1 2 ¯ 1 3 ¯ α ∥ [031] γ . The isothermally-solidified, primary α-Ti grains dominating the entire joint were epitaxially grown, depending on the orientation of the randomly oriented Ti parent grains.

Theoretical studies of the local structures and thegfactors for the tetragonal Ti3+-Vocenters in BaTiO3bulks and thin films

The local structures and the EPR g factors g║ and g┴ are theoretically studied for the tetragonal Ti3+-Vo centers in BaTiO3 bulks and thin films using the perturbation formulas of the g factors for a 3d1 ion in tetragonally elongated octahedra and compressed tetrahedra, respectively, based on the cluster approach. For the Ti3+-Vo center in BaTiO3 bulks, the impurity Ti3+ suffers the displacement away from the oxygen vacancy Vo by about 0.15 Å along the C4 axis due to the electrostatic repulsion of the Vo. Nevertheless, the Ti3+-Vo center in BaTiO3 thin films may exhibit the tetragonally compressed tetrahedron, characterized by the bond angle 55.88° larger than that (≈54.74°) of an ideal tetrahedron. The quite different g factors (especially g anisotropies Δg = g║ − g┴) for the two kinds of samples are discussed, in view of the dissimilar bonding or coordination environments (i.e., incomplete bonding in the thin films may lead to the lower coordination number).

Complete Titanium Substitution by Boron in a Tetragonal Prism: Exploring the Complex Boride Series Ti3−xRu5−yIryB2+x (0 ≤ x ≤ 1 and 1 &lt; y &lt; 3) by Experiment and Theory

Polycrystalline samples and single crystals of four members of the new complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti(3)Co(5)B(2) structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti(3)Ru(2.9)Ir(2.1)B(2)). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti(2)Ru(2.8)Ir(2.2)B(3)). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir-B and Ru/Ir-Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides.

EPR parameters and defect structures of the off-center Ti 3+ ion on the Sr 2+ site in neutron-irradiated SrTiO 3 crystal

The EPR parameters ( g factors and hyperfine structure constants A) for the tetragonal Ti 3+ center in cubic phase and the rhombic Ti 3+ center in tetragonal phase in the neutron-irradiated SrTiO 3 crystals are calculated from the third-order perturbation formulas of EPR parameters for d 1 ions. These low-symmetry Ti 3+ centers in both phases of SrTiO 3 are due to the Ti 3+ ion at “off center” on the Sr 2+ site. From the calculation, the defect models (including the direction and magnitude of the Ti 3+ off-center displacement) of the two Ti 3+ centers in SrTiO 3 are estimated and the EPR parameters of both Ti 3+ centers are reasonably explained on the basis of the defect models. The results are discussed.

Structure and surface morphology of Mn-implanted TiO 2

A study of structure and surface morphology together with magnetic properties of Mn-implanted rutile-type TiO 2 single crystals is performed. Homogenous thin films of about 100 nm with different Mn x Ti 1 − x O 2 ( x = 0.03; 0.05 and 0.07) chemical formula were obtained. The Mn ion implanted surface exhibited a dense microstructure with a nano grain size. The dependence of c/ a axial ratio on manganese content suggests that Mn 3+ species substituted tetragonal Ti 4+. The annealing at 873 K caused changes in surface structure, morphology and roughness. A migration of manganese ions into the rutile single crystal takes place and in certain conditions Ti 2O phase occurs. Mn-implanted samples exhibit room temperature ferromagnetism and a Curie temperature of 680 K. Electron spin resonance analysis evidenced that manganese is incorporated by substitution as magnetically isolated Mn 4+, Mn 3+ and Mn 2+ species. At 0.07% contents the Mn 3+ species may enter in interstitial sites contributing to extinction of substitutional magnetic moment.

Microscopic deformation mechanism of a Ti 66.1Nb 13.9Ni 4.8Cu 8Sn 7.2 nanostructure–dendrite composite

Systematic investigations of the microstructural changes upon compression have been performed in order to elucidate the microscopic deformation mechanisms of the high-strength and ductile Ti 66.1Nb 13.9Ni 4.8Cu 8Sn 7.2 nanostructure–dendrite composite. After 8% deformation, a rotation of β-Ti dendrites is observed during the interaction of slip and shear bands. This rotation leads to the formation of new slip bands in the dendrites. The β-Ti dendrites locally transform into ω phase during the interaction between the newly and the previously formed slip bands. The rotation of the dendrites causes local volume changes at the interfacial areas between the dendrites and the matrix, consisting of a mixture of hexagonal close-packed α-Ti and body-centered tetragonal Ti 2Cu phases. This induces a rotational stress into the nanostructured matrix. After further deformation up to 25%, the shear bands penetrate the dendrite/matrix interfaces, producing extra interfaces. The nanostructured matrix exhibits a sandwiched microstructure in order to accommodate effectively the shear strains. These results suggest that structural coherency of the dendrite/matrix interfaces is important for controlling both the strength and the ductility of the nanostructure–dendrite composite.

Surface nitridation of titanium by pulsed Nd:YAG laser irradiation

Surface nitridation of titanium is an adequate method to improve the hardness and wear resistance of the material. We report experimental results concerning the surface treatment of titanium by pulsed Nd:YAG (λ=1.064 μm) laser irradiation in nitrogen atmosphere. Titanium foils were scanned with constant velocity by high repetition rate (1 kHz) laser beam pulses, and the most appropriate irradiation conditions were determined to obtain titanium nitride surface layers without defects or corrugations. The best results were obtained at laser intensities just under the transition from surface melting to ablation. The obtained layers were characterised by surface profilometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and spectrophotometry. In the XRD spectra of the films the positions of the ( h k l) reflections reproduce the standard data of the tetragonal δ′-Ti 2N phase. In the literature films containing tetragonal Ti 2N phases are described as having better mechanical properties, corrosion and wear resistance in comparison with cubic TiN.

Copper Content Dependence of the Lattice Parameters of Ti(NiCu)&lt;SUB&gt;2&lt;/SUB&gt;

The ternary Ti-Ni-Cu system forms a tetragonal Ti(NiCu) 2 phase with C11 b -type structure, in a wide range of copper content. The copper content dependence of the lattice parameters of the Ti(Ni 1-Y Cu Y ) 2 (0.22 ≤ Y ≤ 0.75) alloys and those of the Ti(NiCu)2 precipitate formed in the Ti 49 (Ni 1-X Cu X ) 51 (0.06 ≤ X ≤ 0.4) alloys, were determined by powder X-ray diffraction. The parameters a and c both exhibit a minimum, but the ratio c/a decreases almost linearly as the copper content increases. The coherency between the matrix and the precipitate becomes worse as the copper content increases. The relation between the copper contents X and Y will be approximated as Y = 1.24X + 0.09. While the X-ray diffraction patterns can be indexed by the C11 b -type structure, diffuse 1/2{110} reflections appear in the electron diffraction pattern. The Vickers microhardness of Ti(NiCu) 2 decreases as the copper content increases.

Titanium-based films deposited using a Nd:YAG pulsed laser

Complex examinations were performed of the structure of films of metallic titanium, titanium nitride and titanium oxide deposited by means of PLD with a Nd:YAG laser. The influence of the deposition parameters on the film morphology was examined. The films revealed a nano-structure of good quality. A new tetragonal Ti(N) phase was revealed in the deposition of metallic titanium in a reactive chamber with an argon atmosphere. The TiN phase was formed during deposition of titanium nitride, independently of the nitrogen flow in the chamber. The transition of oxides from Ti2O via TiO to TiO2 was observed with an increasing flow of oxygen in the chamber for deposition of titanium oxide. TEM examinations of the microstructure in cross-sections of the film revealed a micro- columnar structure. All the examined films were characterised by a strong axial crystallographic preferred orientation on the basis of the measured pole figures. The axial texture was identified within the deposited metallic titanium for the Ti(N) tetragonal phase as well as for the TiO oxide, while the texture was observed in the case of TiN nitride. Measurements of the residual stresses of the first order in the TiN phase, by using the X-ray sin2ψ method, showed stress levels of -5000 to -7000 MPa. The residual stresses measured in the substrate of ferritic steel were about -150 MPa.

Identification of metastable phases: face-centred cubic Ti

First-principles total-energy electronic structure calculations are used to find the epitaxial line of tetragonal Ti, i.e., the line of body-centred tetragonal (bct) structures produced by isotropic epitaxial strain on the (001) plane of tetragonal phases of Ti. An fcc phase and a higher-energy noncubic bct phase are found at minima of the total energy with respect to tetragonal deformations, but the bcc structure is found to be a saddle point of energy. The calculation yields the strained structures, the corresponding stresses, and the elastic stiffness coefficients on the epitaxial line. A segment of the epitaxial line between the two phases is shown to be inherently unstable, so unique meaning can be given to designating a structure as strained fcc Ti. The bulk structure of a film of Ti on Al{001} is shown to be strained fcc Ti, a new phase not on the phase diagram.

Sr13□NbAs11 and Eu13□NbAs11 – Defect Variants of the Ca14AlSb11 Structure with asymmetric [As3]7− anions

AbstractThe novel compounds Sr13NbAs11 and Eu13NbAs11 have been synthesized from SrAs, Eu5As4, Sr, Nb and As in niobium ampoules at 1173–1273 K. The tetragonal tI 200 phases are defect variants of the Ca14AlSb11 structure (space group I41/acd (no. 142); Sr13□NbAs11: a = 1649.8(2) and c = 2214.1(3); Eu13□NbAs11: a = 1632.9(8) and c = 2197.3(8) pm; Z = 8). The structures are built from the cations Sr2+, and Eu2+, respectively, and from the anions [NbAs4]7−, As3−, and the linear polyanion [As3]7−. This polyanion (isosteric to I3−) is asymmetric with d(AsAs) = 273.0 and 346.0 pm (Sr) and 274.7 and 335.6 pm (Eu), respectively. The bond lengths in the tetrahedral anions are d(NbAs) = 250.8 and 251.1 pm. The complete structural arrangement is related to that of Cu2O by forming two interpenetrating networks. The oxygen atoms are substituted by niobium centered As4 tetrahedra, and the Cu atoms are substituted by As6 octahedra (centered by Sr, Eu). The central As atoms of the polyanions connect the nets. Both As networks are enveloped by the remaining cations forming cubes, tetragonal antiprisms and capped trigonal prisms.

Microstructural evolution of the crystallization of a Ti-Si-Nd amorphous alloy

A nanoscale composite of α-Ti and Ti 3Si phases as been produced by annealing the as-quenched amorphous Ti 80Si 20 alloy containing 0.6 wt% Nd. Detailed electron microscopic studies of the crystallization behavior of the amorphous alloy established that very fine particles of α-Ti form first, followed by the precipitation of the predominant bc tetragonal Ti 3Si and a small amount of Ti 5Si 3 compounds. Ultrafine α-Ti crystallites are observed only inside the Ti 3Si phase. The formation and microstructural characterization of the Ti 3Si phase are also presented.

Phase formation and characterization of hard coatings in the TiAlN system prepared by the cathodic arc ion plating method

Hard Ti x N and (Ti 1− x Al x )N films were prepared using the cathodic arc ion plating method. When the ratio of the partial pressure of N 2 to the evaporation rate of titanium was reduced, the resulting phase in the TiN system changed from cubic TiN to tetragonal Ti 2N, and then to h.c.p. α-Ti. When the AIN content in the TiNAlN solid solution was increased, the films, from TiN up to (Ti 0.3Al 0.7)N, exhibited a cubic structure. As the AlN content increased, the lattice parameter monotonically decreased from 4.26 Å for TiN, to 4.16 Å for (Ti 0.3Al 0.7)N. With a further increase in AlN content, (Ti 0.15Al 0.85)N films were found to have a wurtzite structure. It was concluded that the crystal structure of the ternary TiAlN system along with the wide-ranging solubility of AlN in TiN is typical for the isostructural group of cubic titanium-based nitrides. The (Ti,Al)N coatings were stable in air at a temperature of 800°C, whereas the TiN films began to oxidize at a temperature of 550°C. It was found that protective layers of amorphous aluminum oxides formed on top of the (Ti,Al)N films during elevated temperature oxidation tests which protected the film from further oxidation. The crystallized TiO 2 that was formed on the TiN film did not give the same protection. The nicrohardness and wear resistance of the (Ti,Al)N films were also investigated.

Ion beam nitriding of titanium and titanium alloy

Titanium and Ti8A/1Mo1V alloy have been nitrided with an ion beam source of nitrogen or agon and nitrogen, at a total pressure of 2−10×10 −4 torr. The treated surface has been characterized by surface profilometry, X-ray diffractometry, Auger Electron Spectroscopy (AES), and microhardness measurements. It was found that tetragonal Ti 2N phase forms in pure titanium and Ti8A/2Mo1V alloy with traces of AIN in the alloy. Two opposite processes were found to compete during the ion beam nitriding: (a) formation of nitrides in the surface layers; (b) sputtering of the nitrided layers by the ion beam. The highest surface hardness, of about 500 kg mm −2 in titanium and 800 kg mm −2 in Ti8A/1Mo1V, was obtained by nitriding with an ion beam of pure nitrogen at 4.2×10 −4 torr, at beam voltage of 1000 V.

Thermal stability of amorphous Ti-Cu alloys

Amorphous Ti 1− x Cu x alloys were prepared by means of melt spinning in the range 0.28 ⩽ x ⩽ 0.75. The crystallization behaviour of these alloys was studied using differential scanning calorimetry and X-ray diffraction. In most amorphous alloys crystallization proceeded by formation of either the tetragonal Ti 2Cu phase (C11b-type) or the tetragonal γ-TiCu phase (B11-type). Crystallization of the Cu-rich alloys involved a new phase hitherto not reported in the literature. The crystallization temperatures of the amorphous Ti 1− x Cu x, were found to occur around 700 K and to show little variation with concentration. These features are expected on the basis of the hole model proposed earlier. The crystallization temperatures were studied as a function of the heating rate and the results were analysed by means of the Kissinger-Boswell method. The activation energies for crystallization obtained from this analysis increase strongly towards the middle concentration range. This was explained in terms of a temperature-dependent configurational entropy in conjunction with the occurrence of chemical shortrange ordering.

A transmission electron microscopy study of annealed Nb-Ge thin films

Microcrystalline sputter-deposited niobium-germanium films were annealed inside a transmission electron microscope and the microcrystalline-to-crystalline phase transformation was studied. From selected area electron diffraction patterns it was found that, in addition to the A15 Nb 3Ge and other phases expected, two previously unreported phases were present in the crystalline films. These were identified as being analogous to the tetragonal Ti 3P and cubic Cu 3Au phases of the niobium-silicon system.