Electronic spectra of chromate doped 3CdSO4 · 8H2O crystals

The optical absorption spectra of CrO^2-₄ doped 3CdSO₄ · 8H₂O crystals revealed four bands. The two prominent bands at 27, 030 and 36, 360cm^-1 along with the featureless, intense band at 41, 670cm^-1 are assigned to the electronic transition ¹A₁→¹T₂. The lowest energy band at 24,100 cm^-1 is attributed to the orbitally forbidden transition ¹A₁→¹T₁ in accordance with the Molecular Orbital scheme of Viste ang Gray. The spectrum recorded at 80 K exhibited a fine structure superposed on the two prominent bands. The structure is ascribed to the vibrational progression of totally symmetric breathing mode in CrO^2-₄ ion.     

Crystallization kinetics and growth mechanism of Pb(Zr0.52·Ti0.48)O3 nanopowders

In this study, Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were synthesized via sol–gel process. Particle morphology, crystalline phases and thermal behavior were characterized by scanning electron microscopy, X-ray diffraction and simultaneous thermal analyzer, respectively. The X-ray diffraction pattern showed perovskite phase clearly. The non-isothermal activation energy for the perovskite crystallization in Pb(Zr_0.52·Ti_0.48)O₃ gel powders was 224.91 kJ mol^?1. Both growth morphology parameter (n) and crystallization mechanism index (m) are close to 3.0, indicating that the bulk nucleation is dominant in the perovskite PZT formation. To determine dielectric properties, the calcined Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were pressed using uniaxial press. It was found that the Pb(Zr_0.52·Ti_0.48)O₃ disks, by sintering at 1,200 °C for 2 and 10 h, and at 1 kHz frequency, had 966 and 1,490 of the dielectric constant, respectively.     

Peculiarities of Raman spectra and phase states in Pb x Sr1−x TiO3 solid solutions with low lead concentration

Micro-Raman study of Pb _x Sr_{1 ? x} TiO₃ (x = 0.005, 0.01, 0.02, 0.03, or 0.04) solid solutions has been performed in the frequency range 15–1200 cm^?1 at several temperatures in the range 10–300 K. The results obtained suggest that the concentration region x < 0.04 in Pb _x Sr_{1 ? x} TiO₃ solid solutions should most likely be considered as heterophase.     

Synthesis and characterization of (Bi2O3)1−x−y−z(Gd2O3)x (Sm2O3)y(Eu2O3)z quaternary solid solutions for solid oxide fuel cell

Sm₂O₃, Gd₂O₃, Eu₂O₃ triple-doped Bi₂O₃ based quaternary solid solutions were synthesized as a candidate electrolyte material using the solid-state reaction technique. The structural, thermal and electrical conductivity features of the ceramic samples were examined and compared by using X-ray powder diffraction (XRD), thermal gravimetry/differantial thermal analysis (TG/DTA) and the four-point probe technique (4PPT). The result of XRD measurements indicated that the (Bi₂O₃)_{(1−x−y−z)}(Gd₂O₃)_x(Sm₂O₃)_y(Eu₂O₃)_z (x = 10/y = 10/z = 5, 15, 20 mol % and x = 10/y = 5, 10, 15, 20/z = 10 mol %) samples have a stable face-centered cubic δ-phase and mixed phase crystallographic structure. The phase stability was also checked by the DTA evaluations results. The temperature dependent electrical conductivity measurements showed that the highest electrical conductivity was observed for the sample of the (Bi₂O₃)_0.75(Gd₂O₃)_0.10(Sm₂O₃)_0.05(Eu₂O₃)_0.10 system which has a stable and δ-phase was found as 6.67 × 10⁻³ (Ω cm)⁻¹ at 650 °C. This sample can be used as an electrolyte material in the solid oxide fuel cells (SOFCs) which is possible to operate at intermediate temperature ranges. The activation energy was also calculated at a low temperature range (350–650 °C) and high temperature range (above 650 °C). The values for the samples vary from 0.63 eV to 1.08 eV at low temperature and at high temperature they vary from 0.43 eV to 0.75 eV.     

Intersite cation partitioning in natural and synthetic alpha-(Fe,Mn)2O3 (bixbyite) solid solutions determined from57Fe Mössbauer spectroscopy

The partitioning of Fe³⁺ and Mn³⁺ between the 8b and 24d crystallographic sites in samples of alpha-(Fe, Mn)₂O₃ solid solutions was determined from⁵⁷Fe Mössbauer spectroscopy measurements at 298 K. In the case of synthetically prepared samples, we find that with increasing iron content and temperature of equilibration, Fe³⁺ preferentially enters the more distorted 24d sites. However, the intersite cation distribution coefficient (K _D) is only a function of the temperature of equilibration, and can therefore be used to estimate the temperature of formation of naturally occurring bixbyite. Using this technique, the temperature of formation of bixbyite samples from the Postmasburg manganese field in South Africa was calculated to be between 315 and 370 C. This is in good agreement with values obtained from other techniques, suggesting that it may be possible to use the intersite cation distribution in bixbyite as a geothermometer.     

Photoacoustic spectra of Fe3+ and Cr3+ in lithium chromo-ferrites,Li0.5Fe2.5−xCrxO4 (0≤x≤2.5)

Photoacoustic spectra of polycrystalline Li_0.5Fe_2.5−xCr_xO₄ (x=0, 0.5, 1.25, 2.0 and 2.5) and LiFeO₂ have been investigated at 300K in the wavelength range 200–2500 nm. The spectra of x=0 composition arises from octahedral and tetrahedral Fe³⁺ ions in the spinel lattice. The Crsubstituted Li-ferrite phases exhibit broad maxima in the range 1400–1600nm and these are attributed to tetrahedral Cr³⁺ present in these phases besides the usual octahedral Cr³⁺ ions. The results are discussed in the light of recent work on tetrahedral Cr³⁺. The results of ferrimagnetic resonance spectra of Li ferrites and their Cr-substituents are also reported and correlated with photoacoustic spectra.     

Raman spectra and restructurizations in the system of solid solutions NaTa y Nb1−y O3

By recording the Raman spectra, concentrational restructurizations in the system of solid solutions NaTa_yNb_1−yO₃ were investigated. The regions of relatively stable existence of solid solutions (y<0.2, y>0.8) and the region of a rather high disordering (0.2<y<0.9) with maximum deformation of the elementary cell at y=0.5 have been revealed. It is found that at y=0.5 a concentrational phase transition is observed, and at y ∼ 0.25 and 0.8 concentrational restructurizations occur. It is shown that the octahedral anions of BO₆ are centrosymmetric when y<0.2 and y>0.9, and the system of solid solutions NaTa_yNb_1−yO₃ is antiferroelectric when y<0.2. In the range of concentrations 0.2<y< 0.9, the structure of NaTa_yNb_1−yO₃ is characterized by the presence of polar clusters. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 192–198, March–April, 2000.     

Ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramics under compressive stress

Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN system were investigated. The ceramics with a formula (1−x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Zn_1/3Nb_2/3)O₃ or (1−x)PZT–(x)PZN (x = 0.1–0.5) were prepared by a conventional mixed-oxide method. The ferroelectric properties under the compressive stress of the PZT–PZN ceramics were observed at the stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (P_sat), the remnant polarization (P_r), and the coercive field (E_c) decreased. These results were interpreted through the non-180° ferroelastic domain switching processes.     

Infrared phonon spectra of 3d-metal doped YBa2(Cu1-x M x )3O7-δ

Infrared (IR) absorption spectra of doped YBa₂(Cu_1–x M _x )₃O_7–, with M representing Co, Fe, Ni, and Zn were observed as a function of concentrationx. TheB _1u IR mode at 580 cm^–1 was observed for all samples which were in the orthorhombic phase, which includes all the Ni and Zn doped samples and the lower concentrations (x<2.5%) for Fe and Co samples. The tetragonal phase of Co and Fe systems (x%>2.5%) shows three new IR modes at 655 cm^–1, 340 cm^–1, and 175 cm^–1. The frequency of the B_1u mode at 580 cm^–1 remains unchanged for all the Ni and Zn concentrations. In contrast, this mode shows a strong monotonic frequency softening with increase in Co substitution, while in the Fe-system it shows a comparable monotonic mode softening for 3%x%0%, and then remains unchanged for 12%x%3%. These observations indicate that Fe and Co substitute on the Cu(1) sites, whereas Ni and Zn most likely substitute on Cu(2) sites. We attribute the difference in the mode softening for Co and Fe to different Cu(1) local environments for these two elements. Indication for a chain-plane charge transfer based on our results is also discussed.     

Synthesis and physicochemical properties of Li2 Me x Zr1 − x O3 − δ (Me = Nb,Ti; x = 0.05, 0.1) solid solutions

Complex lithium metallates Li₂ Me _x Zr_{1 ? x} O_{3 ? δ} (Me = Nb, Ti, x = 0.05, 0.1) with iso-and heterovalent substitutions for Zr⁴⁺ ions in lithium zirconate are synthesized for the first time using a citrate technique. The inclusion of Ti⁴⁺ and Nb⁵⁺ ions in the crystal structure of Li₂ZrO₃ is confirmed by means of X-ray diffraction and NMR. It is shown that in the temperature range of 750–820 K, Li₂Ti_0.1Zr_0.9O₃ solid solution has higher conductivity than phases of undoped lithium zirconate.     

Reduction of hematite with ethanol to produce magnetic nanoparticles of Fe3O4, Fe1 − x O or Fe0 coated with carbon

The production of magnetic nanoparticles of Fe₃O₄ or Fe⁰ coated with carbon and carbon nanotubes was investigated by the reduction of hematite with ethanol in a Temperature Programmed Reaction up to 950°C. XRD and Mössbauer measurements showed after reaction at 350°C the partial reduction of hematite to magnetite. At 600°C the hematite is completely reduced to magnetite (59%), wüstite (39%) and metallic iron (7%). At higher temperatures, carbide and metallic iron are the only phases present. TG weight losses suggested the formation of 3–56 wt.% carbon deposits after reaction with ethanol. It was observed by SEM images a high concentration of nanometric carbon filaments on the material surface. BET analyses showed a slight increase in the surface area after reaction. These materials have potential application as catalyst support and removal of spilled oil contaminants.     

Correlation of dielectric properties,Raman spectra and calorimetric measurements of β-cyclodextrin-polyiodide complexes (β-cyclodextrin)2 ·BaI7 ·11H2O and (β-cyclodextrin)2 ·CdI7·15H2O

The frequency and temperature dependence of real and imaginary parts of the dielectric constant (ε′,?ε″), the phase shift (?) and the ac-conductivity (σ) of polycrystalline complexes (β-CD)₂·BaI₇·11H₂O and (β-CD)₂·CdI₇·15H₂O (β-CD?=?β-cyclodextrin) has been investigated over the frequency and temperature ranges 0–100?kHz and 140–420?K in combination with their Raman spectra, DSC traces and XRD patterns. The ε′(T), ε″(T) and ?(T) values at frequency 300?Hz in the range T<330?K show two sigmoids, two bell-shaped curves and two minima respectively revealing the existence of two kinds of water molecule, the tightly bound and the easily movable. Both complexes show the transition of normal hydrogen bonds to flip-flop type at 201?K. In the β-Ba complex most of the eleven water molecules remain tightly bound and only a small number of them are easily movable. On the contrary, in the β-Cd case the tightly bound water molecules are transformed gradually to easily movable. Their DSC traces show endothermic peaks with onset temperatures 118°C, 128°C for β-Ba and 106°C, 123°C, 131°C for β-Cd. The peaks 118°C, 106°C, 123°C are related to the easily movable and the tightly bound water molecules, while the peaks at 128°C, 131°C are caused by the sublimation of iodine. The activation energy of Ba²⁺ ions is 0.52?eV when all the water molecules exist in the sample and 0.99?eV when the easily movable water molecules have been removed. In the case of β-Cd the corresponding activation energies are 0.57?eV and 0.33?eV. The Raman peaks at 179?cm^?1, 170?cm^?1 and 165–166?cm^?1 are due to the charge transfer interactions in the polyiodide chains.     

Effect of Li2O on the structure,electrical and dielectric properties of xLi2O·(20−x)CaO·30P2O5·30V2O5·20Fe2O3 glasses

Glasses of the general formula xLi₂O·(20?x)CaO·30P₂O₅·30V₂O₅·20Fe₂O₃ with x=0, 5, 10, 15 and 20 mol% were prepared; IR, density, electrical and dielectric properties have been investigated. Lithia-containing glasses revealed more (P₂O₇)^4?, FeO₆, V–O^? and PO^? groups and mostly have lower densities than those of lithia-free ones. The electrical properties showed random behavior by replacing Li₂O for CaO, which has been assigned to the change of the glass structure. The results of activation energy and frequency-dependent conductivity indicate that the conduction proceeds via electronic and ionic mechanisms, the former being dominant. The mechanism responsible for the electronic conduction is mostly thermally activated hopping of electrons from Fe(II) ions to neighboring Fe(III) sites and/or from V⁴⁺ to V⁵⁺. The dielectric constant (ε′) showed values that depend on the structure of glass according to its content of Li₂O. The (ε′) values are ranging between 3 and 41 at room temperature for 1 kHz, yet at high temperatures, glass with 20 mol Li₂O exhibits values of 110 and 3600 when measurement was carried out in the range 0.1–1 kHz, and at 5 MHz, respectively.     

Superlattice structures in solid solution of high-Tc YBa2Cu3O7−δ and (Pb,Cu)Sr2(Ca,Y)Cu2O7−δ superconductors

A complete solid solution range exists between the systems YBa₂Cu₃O_7−δ and (Pb,Cu)Sr₂(Ca,Y)Cu₂O_7−δ has been found with general stoichiometry (Pb_0.75xCu_1−0.75x)(Sr_2xBa_2−2x)(Ca_0.5xY_1−0.5x)Cu₂O_7−δ. Energy dispersive spectrometry and X-ray diffraction identified that a true solid solution exists. Superlattice structures observed by electron diffraction across the solid solution range have a modulation range have a modulation periods along a* which can be varied by altering both the compositional parameter x and the overall oxygen content. The existence of these superlattices infers that the solid solution is non-random and therefore thermodynamically non-ideal. The superconducting transition temperatures, T_c, across the solid solution range are also strongly dependent on the composition, x, but no direct relationship with the modulation period has been established. From these studies it may be concluded that the solid solution between known superconductors is possible, although involving some partial ordering of the lattice, but ordering of cations in the rock-salt to charge reservoir layer is not a significant factor in determining the superconducting properities, which depend more closely on the overall composition and hence on the ability of the charge reservoir layer to transfer charge to the superconducting layers.     

Elastic properties of (Pb y Sn1−y )2P2S6 solid solutions

Elastic properties of (Pb _y Sn_1?y )₂P₂S₆ solid solutions were studied using Brillouin scattering technique. Different scattering geometries were used for sound velocities determination that make it possible to find all components of the stiffness tensor. The concentration dependencies of volume compressibility, the Grüneisen parameter and Debye temperature were investigated. The results obtained were used to analyze chemical bonding with substitution of tin by lead at room temperature in the crystals under consideration.     

Effects of Zr/Ti ratio on dielectric and ferroelectric properties of 0.8Pb(ZrxTi1−x)O3–0.2Pb(Co1/3Nb2/3)O3 ceramics

The influences of Zr/Ti ratio on electrical properties of the 0.8Pb(Zr_xTi_1−x)O₃–0.2Pb(Co_1/3Nb_2/3)O₃ ceramics prepared by a mixed-oxide method (with x = 0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary composition in this system. With XRD analysis, the crystal structure of dense specimens appeared to change gradually from tetragonal to rhombohedral with increasing Zr content. The dielectric properties measurements showed a maximum dielectric constant at x = 0.50, while the transition temperature decreased with increasing Zr content in the system. Moreover, all ceramics showed diffused phase transition behaviors with a minimum diffusivity at x = 0.50. In addition, the Polarization–Electric field (P–E) hysteresis loops of the ceramic systems also changed significantly with the Zr content. Interestingly, the loop squareness parameter reached maximum around x = 0.50. Other ferroelectric hysteresis parameters showed noticeable change at x = 0.50. These results clearly showed the significance of Zr/Ti ratio in controlling the electrical properties of the PZT–PCN ceramic systems.     

Study of critical exponents in doped La2/3Ca1/3Mn1-y Fe y O3 (y = 0, 0.03) manganite films

In this work, we investigated close to the Curie temperature T _C the critical exponents of the magnetization of doped manganite La_2/3Ca_1/3Mn_0.97Fe_0.03O₃ (LCMFO) thin films, as well as undoped La_2/3Ca_1/3MnO₃ (LCMO). Using a T _C distribution given by the intrinsic magnetic inhomogeneities in these ferromagnets enables the determination of β and δ critical exponents [corresponding to M(T) and M(H) respectively], average Curie temperature < T _C > , and the T _C distribution width, ΔT _C. Additionally, we extracted the critical exponent η = βδ from the fits of ΔT _C as a function of the external applied magnetic field. We found a value of 1.74 ± 0.09 for this exponent, close to that reported in undoped La_2/3Ca_1/3MnO₃ thin films. Even though the substitution effects of the Mn ions by Fe affect the magnetotransport and structural properties of LCMO system, these results suggest that around T _C, the magnetic phase transition, governed by the critical exponents, is similar in both magnetic systems, and belongs to the same universality class.     

Polarization Kinetics in Transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 Ceramic

Physics of the Solid State - The polarization kinetics in a transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 ferroceramic is investigated in the electric fields of 0 &lt; E &lt; 6...