Tetragonal Component Research Articles

Long-Term Oxidation Susceptibility in Ambient Air of the Semiconductor Kesterite Cu2ZnSnS4 Nanopowders Made by Mechanochemical Synthesis Method.

The often overlooked and annoying aspects of the propensity of no-oxygen semiconductor kesterite, Cu2ZnSnS4, to oxidation during manipulation and storage in ambient air prompted the study on the prolonged exposure of kesterite nanopowders to air. Three precursor systems were used to make a large pool of the cubic and tetragonal polytypes of kesterite via a convenient mechanochemical synthesis route. The systems included the starting mixtures of (i) constituent elements (2Cu + Zn + Sn + 4S), (ii) selected metal sulfides and sulfur (Cu2S + ZnS + SnS + S), and (iii) in situ made copper alloys (from the high-energy ball milling of the metals 2Cu + Zn + Sn) and sulfur. All raw products were shown to be cubic kesterite nanopowders with defunct semiconductor properties. These nanopowders were converted to the tetragonal kesterite semiconductor by annealing at 500 °C under argon. All materials were exposed to the ambient air for 1, 3, and 6 months and were suitably analyzed after each of the stages. The characterization methods included powder XRD, FT-IR/UV-Vis/Raman/NMR spectroscopies, SEM, the determination of BET/BJH specific surface area and helium density (dHe), and direct oxygen and hydrogen-content analyses. The results confirmed the progressive, relatively fast, and pronounced oxidation of all kesterite nanopowders towards, mainly, hydrated copper(II) and zinc(II) sulfates, and tin(IV) oxide. The time-related oxidation changes were reflected in the lowering of the energy band gap Eg of the remaining tetragonal kesterite component.

The piezoelectric properties of transparent 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3:Pr3+ ceramics

The enhancement of both transparency and piezoelectric properties in transparent ferroelectric ceramics is a challenge. In this work, we prepared transparent 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3:xPr3+ ceramics by oxygen atmosphere sintering together with hot pressing sintering. When x = 1.5 mol%, a transparency of 68% @ 900 nm (close to the theoretical value ~71%) was achieved, and the piezoelectric properties increased to twice as much as those in undoped ceramics (x = 0). The small average domain size (below 200 nm) that far below the visible light wavelength was believed to benefit light transmittance. Meanwhile, the minute amount of tetragonal component induced by Pr3+ irons, was supposed to be responsible for the improved piezoelectric properties. These merits make Pr3+-doped 0.75PMN-0.25PT transparent ceramics promising functional materials for transparent piezoelectric devices.

Neutron-diffraction study of the cubic-tetragonal phase structural transition in the single crystals of the solid solutions of zirconium and yttrium oxides

Objectives. The determination of the phase relations, crystallographic characteristics, microstructure features, and atomic crystal structure of zirconium oxide crystals that are partially and completely stabilized by yttrium oxide additives, and the identification of the crystallographic and crystal-chemical correlations with the physicochemical properties of single crystals.Methods. The neutron structure of the crystals was studied using the neutron time-of-flight and constant wavelength methods using a high-resolution Fourier diffractometer on the IBR-2 pulsed fast reactor and a four-circle neutron diffractometer “Syntex.” Single crystals were grown by directed crystallization from the melts of mixtures (1 − х)ZrO2 ∙хY2O3 , х = 0.03 and х = 0.12 with different growth rates (10 and 40 mm/h).Results. It was observed that when growing single crystals with x = 0.03–0.05, the crystal was stratified into cubic and tetragonal phases, and the ratio between the phases depended on the growth rate. At a growth rate of 40 mm/h, the content of the cubic phase was insignificant. In the crystals of partially stabilized zirconium dioxide (ZrO2) with the additions of 3 mol % Y2O3, the coherent coexistence of cubic and tetragonal phases was established, and the twin law for a tetragonal component (rotation of unit cell axis by 90° around the a (b) axis) that was observed during the phase transition from high-temperature cubic phase to tetragonal phase was determined. For the fully stabilized zirconium oxide of the cubic symmetry (with 12 mol % Y2O3), the 0.3 Å displacements of oxygen atoms from their partial structural positions in the directions [100] and [111] were determined. These displacements correlated with the directions of the ion transport.Conclusions. Previous studies have shown that the ratio between the cubic and tetragonal phases of the single crystals of the ZrO2 –Y2O3 system depends on the growth rate of the single crystals. The content of Y2O3 in the cubic and tetragonal phases of a single crystal was determined using the non-destructive neutronography method on the same volume sample of a solid solution of this system. Moreover, the displacements of oxygen atoms from the main position of the crystal were determined.

SHI induced tetragonal tracks in natural zirconia

We describe the observed tetragonal nature of individual ion tracks produced in natural monoclinic zirconia (ZrO2) as a result of 167 MeV Xe irradiation at room temperature in the non-overlapping track regime. Direct observation by transmission electron microscopy of the tetragonal latent tracks reveals a non-continuous structure consisting of segments which are approximately 30 nm in length and angled 9° w.r.t the ion direction. This angle is consistent with the angular difference for the unit cells of the two phases. The tracks are shown to have rectangular cross sections with dimensions of the order 2.5 nm. The tetragonal component orientation relative to the parent monoclinic orientation is in agreement with the proposed variants by Kelly et al. The tetragonal phase transforms back to the monoclinic phase in the range of 200–350 °C which is well below the bulk transformation temperature of about 1100 °C.

Local Structure of Zr(OH)4 and the Effect of Calcination Temperature from X-ray Pair Distribution Function Analysis.

Analysis of X-ray pair distribution function data has provided a detailed picture of the local structure of amorphous Zr(OH)4 and its thermal decomposition into ZrO2. In the untreated phase, the Zr atoms tend to be coordinated by six or seven oxygen atoms. The Zr centered polyhedra connect to each other primarily by sharing edges, but also with a significant amount of corner sharing, to form two-dimensional sheets in which the Zr are connected to an average of about five other Zr. This local structure is related to the structure of monoclinic ZrO2 and can be derived from it by removing certain Zr neighbors to form sheets and reduce the corner to edge sharing ratio. The maximum correlation length in Zr(OH)4 is about 12 Å. Heating up to 125 °C results in significant water loss but does not alter the network of Zr and bridging O atoms. Additional water loss caused by heating to 250 °C triggers a reorganization into a new type of amorphous phase with a three-dimensional network and a greater number of Zr-Zr neighbors. Further heating to 330 °C causes crystallization into a mixture of tetragonal and monoclinic ZrO2, with the minor tetragonal phase having a smaller average domain size. The tetragonal component vanishes by 900 °C.

Measurement of the B1g and B2g components of the elastoresistivity tensor for tetragonal materials via transverse resistivity configurations.

The elastoresistivity tensor mij,kl relates changes in resistivity to strains experienced by a material. As a fourth-rank tensor, it contains considerably more information about the material than the simpler (second-rank) resistivity tensor; in particular, for a tetragonal material, the B1g and B2g components of the elastoresistivity tensor (mxx,xx - mxx,yy and 2mxy,xy, respectively) can be related to its nematic susceptibility. Previous experimental probes of this quantity have focused exclusively on differential longitudinal elastoresistance measurements, which determine the induced resistivity anisotropy arising from anisotropic in-plane strain based on the difference of two longitudinal resistivity measurements. Here we describe a complementary technique based on transverse elastoresistance measurements. This new approach is advantageous because it directly determines the strain-induced resistivity anisotropy from a single transverse measurement. To demonstrate the efficacy of this new experimental protocol, we present transverse elastoresistance measurements of the 2mxy,xy elastoresistivity coefficient of BaFe2As2, a representative iron-pnictide that has previously been characterized via differential longitudinal elastoresistance measurements.

Blue absorption and red emission of Bi2+ in solids: strongly spin-orbit coupled 6p levels in low symmetry fields.

Wave function embedded cluster ab initio calculations on a (BiO8)(14-) cluster under the effects of a high symmetry Oh confinement potential are used to study the energies of the (2)P1/2, (2)P3/2(1), and (2)P3/2(2) spin-orbit coupling levels of the 6s(2)6p configuration of Bi(2+) in Oh, D4h, D2h, D4, D2d, D2, S4, C4v, C4, C3v, C2v, C2, Cs, and C1 fields, together with the (2)P1/2→(2)P3/2(1) and (2)P1/2→(2)P3/2(2) absorption oscillator strengths and the (2)P3/2(1) radiative lifetime. These levels are responsible for the blue absorptions and the red-orange emissions produced when Bi(2+) is doped in borates, phosphates, sulphates, and other hosts. It is found that the splitting of (2)P3/2 is mainly due to the tetragonal D4h and orthorhombic D2h components of the actual field. It is enhanced by Bi going towards two or four ligands. The intensities of the (2)P1/2→(2)P3/2(1) and (2)P1/2→(2)P3/2(2) absorptions are mostly induced by the Bi displacements and by tetragonal scalenoidal D2d fields. The most favorable fields for a large splitting of the (2)P3/2 level that can drive a red shift of the (2)P3/2(1) →(2)P1/2 emission are the C2v and Cs fields resulting from the combination of D2h orthorhombic fields and Bi approaching two or four ligands on the main orthorhombic planes.

Mössbauer study of fine structure features of equiatomic FePd alloy after severe plastic deformation and ordering annealing

Abstract Using Mossbauer spectroscopy based on modern methods of processing spectra, new fine features of the structure of equiatomic alloy FePd, which is formed upon the А 1 → L 1 0 phase transformation in the course of severe plastic deformation by torsion and annealing for ordering at the temperature Т = 450 o С, have been studied. It is shown that the structure of the alloy in the as-deformed state cannot be treated as a homogeneous solid solution; it is more likely to consider it as an alternation of disordered regions that are different in composition and in the sign and degree of tetragonal distortions of the initial fcc lattice. Already at early stages of ordering annealing, there are detected low-symmetry regions, inhomogeneous in composition and in the degree of ordering, with tetragonal distortions of the same sign but essentially different in magnitude. These regions can be identified as the structure constituents of the A 6 and L 1 0 type with the tetragonal lattice. Such a multi-phase structure is retained even after a long-time ( t ann = 40 h) annealing. A conclusion is made that the equilibrium tetragonal L 1 0 phase is formed as a result of long-term redistribution of Fe atoms between the initial cubic and newly formed tetragonal components. The effect of the fine-structure peculiarities on the coercivity of the FePd alloys is considered.

140 H/D Isotopomers Identified by Long-Range NMR Hyperfine Shifts in Ruthenium(III) Ammine Complexes. Hyperconjugation in Ru–NH3Bonding

(1)H NMR spectra of the paramagnetic cyanide-bridged mixed-valence compound [(η(5)-C5H5)Fe(CO)2(μ-CN)Ru(NH3)5](CF3SO3)3 (I) have been obtained in several solvents. When traces of partially deuterated water are present, instead of a single cyclopentadienyl (Cp) resonance shifted by the hyperfine interaction, numerous well-resolved resonances are observed. The spectra were simulated satisfactorily by giving the appropriate statistical weight to 140 possible H/D isotopomers formed by deuteration in the five ruthenium(III) ammine ligands. The proliferation of distinct resonances occurs because (a) the hyperfine shifts (HSs) due to each sequential deuteration in a single ammine are different and (b) while deuteration in an ammine cis to the cyanide bridge causes a downfield shift, in the trans ammine it causes an upfield shift that is nearly twice as large. All of these shifts exhibit a 1/T dependence, but temperature-independent components, due to large second-order Zeeman effects at the Ru(III) center, are also present. Combining the results of density functional theory calculations with data from metal-metal charge-transfer optical transitions and with the effect of solvent-induced NMR HSs, it is argued that Fermi contact shifts at the Cp protons are insignificant compared to those due to the dipolar (pseudocontact) mechanism. Analytical expressions are presented for the dependence of the HS on the tetragonal component of the ligand field at the Ru(III) ion. The tetragonal field parameter, defined as the energy by which the 4d(xy) orbital exceeds the mean t(2g) orbital energy, was found to be 147, 52, and 76 cm(-1), in dimethylformamide, acetone, and nitromethane, respectively. The effects of deuteration show that there is a significant component of hyperconjugation in the Ru-ammine interaction and that ND3 is a weaker π donor than NH3. A single deuteration in an axial ammine increases the tetragonal field parameter (ν) by +2.8 cm(-1), resulting in a HS of -37 ppb in the Cp proton resonance, whereas a single deuteration in an equatorial ammine decreases the field by -1.5 cm(-1) with a HS of +20 ppb, despite a nominal separation of seven chemical bonds. We analyze the origin of this remarkable sensitivity, which relies on the favorable characteristics of the Ru(III) low-spin t(2g)(5) configuration, having a spin-orbit coupling constant ζ ≈ 950 cm(-1).

Nonlinear Optical Susceptibility of Tetragonal BaTiO<sub>3</sub>

In the framework of the vibronic theory of ferroelectricity for the transparency region of tetragonal BaTiO3 components and of nonlinear optical susceptibility responsible for the second harmonic generation and the optical rectification are calculated. Selection rules for dipole transitions in the Γ point of the first Brilouin zone are extended over the whole zone. Calculations are confined to lowest order in expansion of susceptibilities in power series of low symmetry lattice distortion. Numerical values of susceptibilities have experimentally observed order of magnitude. The spectral behavior of and is calculated as well.

UV–Vis absorption study of some tetragonal chromium (III) complexes

A UV–Vis absorption study was performed in order to elucidate the electronic energy levels of three tetragonal chromium (III) complexes, namely trans-[Cr(en) 2(CN) 2]ClO 4, trans-[Cr(cyclam)(CN) 2]ClO 4, and trans-[Cr(NH 3) 4(CN) 2]ClO 4. The absorption spectra of the preceding complexes have been analyzed via Gaussian analysis to locate the quartet band maxima of the tetragonal components. The deconvoluted band maxima were then fitted with the tetragonal energy matrices of d 3 configuration with full configuration interaction, neglecting spin–orbit interaction. The ligand field parameters D q, D t, and D s along with the electron correlation parameters have been extracted via the fitting procedure. The significance of these parameters and the translated angular overlap model parameters has been discussed. We have also uncovered in the spectrum of the ethylenediamine complex the low intensity doublet absorption bands and a high intensity charge transfer band which have been tentatively assigned.

Size effect on crystal structure and chemical bonding nature in BaTiO3 nanopowder

The size effect on the crystal structure including the chemical bonding nature has been investigated for several kinds of BaTiO3 nanopowder with the particle sizes down to 50 nm in diameter, by means of powder diffraction using high-energy synchrotron radiation. The Rietveld refinement reveals that the BaTiO3 nanopowder consists of tetragonal and cubic structure components at 300 K. The feature of coexistence can be illustrated by the core/shell model for the particle, in which the shell with a cubic structure covers the core with a tetragonal structure. The thickness of the cubic shell is almost constant irrespective of the particle sizes, and is estimated as approximately 8 nm. Hence, the critical particle-size, where the entire particle is covered with the cubic shell, is suggested as 16 nm. The charge density distributions of the BaTiO3 nanopowder in the cubic phase at 410 K are revealed by the maximum entropy method. Changes in the bonding electron density and the ionic valence expected are not observed clearly even in the 50 nm crystal compared with the bulk crystal.

NMR paramagnetic relaxation due to the S=5∕2 complex, Fe(III)-( tetra-p -sulfonatophenyl)porphyrin: Central role of the tetragonal fourth-order zero-field splitting interaction

The metalloporphyrins, Me-TSPP [Me=Cr(III), Mn(III), Mn(II), Fe(III), and TSPP=meso-(tetra-p-sulfonatophenyl)porphyrin], which possess electron spins S=3/2, 2, 5/2, and 5/2, respectively, comprise an important series of model systems for mechanistic studies of NMR paramagnetic relaxation enhancement (NMR-PRE). For these S>1/2 spin systems, the NMR-PRE depends critically on the detailed form of the zero-field splitting (zfs) tensor. We report the results of experimental and theoretical studies of the NMR relaxation mechanism associated with Fe(III)-TSPP, a spin 5/2 complex for which the overall zfs is relatively large (D approximately = 10 cm(-1)). A comparison of experimental data with spin dynamics simulations shows that the primary determinant of the shape of the magnetic relaxation dispersion profile of the water proton R1 is the tetragonal fourth-order component of the zfs tensor. The relaxation mechanism, which has not previously been described, is a consequence of zfs-induced mixing of the spin eigenfunctions of adjacent Kramers doublets. We have also investigated the magnetic-field dependence of electron-spin relaxation for S=5/2 in the presence of a large zfs, such as occurs in Fe(III)-TSPP. Calculations show that field dependence of this kind is suppressed in the vicinity of the zfs limit, in agreement with observation.

Electron paramagnetic resonance study of Fe3+ ions at octahedral and tetrahedral mirror symmetry sites in the LiScGeO4 crystal

An electron paramagnetic resonance (EPR) study of a synthetic single crystal of LiScGeO4 doped with Cr ions carried out earlier at the X- and Q-bands at 300, K has indicated additional weak lines. A detailed analysis of these EPR lines, which were tentatively attributed to the Fe3+ ions at two different mirror symmetry sites, is presented in this paper. The angular dependences in the three crystallographic planes were resolved by fitting the two distinct spectra denoted Fe3+(I) and Fe3+(II) with a spin Hamiltonian (S=5/2) of monoclinic symmetry. The rank-4 crystal field tensors at tetrahedral and octahedral sites were calculated with the point-charge model to determine the principal axis orientations of their cubic, tetragonal and trigonal components. A comparative analysis of the zero-field splitting tensors and the crystal field ones indicates that Fe3+(I) ions substitute for Sc3+ at octahedral sites and Fe3+(II) ions substitute for Ge4+ at tetrahedral sites with no significant distorition of the coordination polyhedra in the structure of LiScGeO4.

Magnetic properties of complex d1 and d5 ions: crystal field model and Jahn–Teller effect

In this paper, the low lying levels of d1 and low-spin d5 metal complexes possessing ground 2T2 term are considered. Strong spin–orbital interactions is taken into account along with the axial (trigonal or tetragonal) component of the crystal field. In the framework of the semi-classic adiabatic approximation, vibronic Jahn–Teller and pseudo Jahn–Teller interactions acting within the ground manifold are also considered. The influence of the low-symmetry crystal fields, covalence reduction factor, spin–orbital and Jahn–Teller interactions on the anisotropy of g-factors, temperature independent paramagnetic contributions, and magnetic susceptibility is elucidated.

Tetragonal and rhombohedral induced polar order fromthe relaxor state of PbZn1/3Nb2/3O3

Structural and dielectric characterizations of the relaxor ferroelectric PbZn1/3Nb2/3O3(PZN) were carried out on single crystals in the temperature range ofthe dielectric anomaly (370 K < T < 440 K),under dc electric field applied along [001]-and [111]-directions. Twoferroelectric phases, tetragonal (T) and rhombohedral (R), can be fieldinduced in this temperature range, the symmetry of which depends onthe direction of the applied field, [001] and [111] respectively. E–Tdiagrams were built and interpreted under the consideration of polar nano-regions(PNRs) with a prominent tetragonal component. These PNRs prevent the onset of amonodomain state when the field is applied along [111] and explain the features ofPZN for an applied field along [001]: large lattice strain, easy onset of the T phaseand suppression of the dielectric relaxation for E ≥ 1.5 kV cm−1.The microscopic origin of these PNRs can be discussed in relation with recentnuclear magnetic resonance and structural results reported in other isomorphousrelaxors.

An analysis of electronic bands of Cr 3+ in tetragonal complexes

The complete interaction matrices are used to calculate the absorption energy levels of Cr 3+ ion in a ligand field of D 4 h symmetry and the results are compared with the recently available experimental spectra of Cr( l -his) 2.( NO 3) . The two strong, broad bands observed at 20,760 and 26,820 cm −1 are attributed to the spin-allowed electronic transitions 4 B ̂ 1[t 2 3 4A 2]→ 4 E ̂ [t 2 2( 3T 1)e 4T 2] and 4 A ̂ 2[t 2 2( 3T 1)e 4T 1] , respectively. The group of two weak lines at lower energies are assigned to the spin-forbidden transitions 4 B ̂ 1[t 2 3 4A 2]→ tetragonal components 2 A ̂ 1[t 2 3 2E] and 2 B ̂ 1[t 2 3 2E] within the ground configuration t 2 3 . The wave functions with three largest components for each calculated electronic level are also given. These assignments of experimental levels give values of the Hamiltonian parameters (in cm −1) as B=538, C=33525, ρ=203, μ=−156, Dq=2079.

Composite Structure of BaTiO3Nanoparticle Investigated by SR X-Ray Diffraction

The size effects on the crystal structure and phase transitions have been investigated for BaTiO 3 fine particles of 700, 400, 300 and 100 nm size, by means of powder diffraction using synchrotron radiation (SR) high-energy X-rays. The Rietveld refinement reveals that the BaTiO 3 fine particles consist of tetragonal and cubic structure components at 300 K. The structure model indicating that the cubic BaTiO 3 shell covers the tetragonal BaTiO 3 core is examined. The thickness of the cubic shell is estimated at approximately 8 nm, which is almost constant irrespective of particle sizes, and the volume ratio of the cubic component increases with decreasing the particle size. Successive phase transitions are detected even in 100 nm size particles, where only the tetragonal component undergoes the phase transition.

Structural study of perovskite-type fine particles by synchrotron radiation powder diffraction

The crystal structures of BaTiO3 and PbTiO3 fine particles have been investigated by powder diffraction using synchrotron radiation high energy X-rays. It is revealed that a BaTiO3 fine particle essentially consists of tetragonal and cubic structure components at 300 K, whereas a PbTiO3 fine particle consists of a tetragonal structure. Adopting a structure model for the BaTiO3 particle that a cubic shell covers a tetragonal core, the thickness of cubic BaTiO3 shell is estimated at almost constant irrespective of particle sizes. Successive phase transitions are detected in 100 nm particles of BaTiO3 near the phase-transition temperatures of a bulk crystal. The changes in diffraction profiles are small, but they are apparent for a most up-to-date powder diffractometry.

Thermal Spray Yttria-Stabilized Zirconia Phase Changes during Annealing

Phase stability of thermal barrier deposits made from yttria partially stabilized zirconia (Y-PSZ) is a requirement for extended service lifetime. The response of Y-PSZ plasma-sprayed deposits to annealing at 1000, 1200, and 1400 °C with times from 1 to 1000 h has been evaluated using the Rietveld analysis of neutron diffraction data. Results show that the yttria concentration of the as-sprayed tetragonal zirconia component generally decreased with increasing annealing temperature and time. As the yttria content in the tetragonal phase approached a limiting concentration, about 3.5 mol.% of YO1,5, the tetragonal phase transformed into monoclinic phase on cooling. An increase in monoclinic phase content was clearly observed after annealing for 24 h at 1400 °C and was nearly 35% after 100 h at 1400 °C. A similar trend was observed at 1200 °C for longer annealing times, with monoclinic phase formation beginning after 400 h. At 1000 °C, experimental times were not sufficient for monoclinic phase to form, although a decrease in the yttria concentration in the tetragonal phase was observed.