Relaxor behaviour of (Ba0·5Sr0·5)(Ti0·6Zr0·4)O3 ceramics

Ba_0·5Sr_0·5Ti_0·6Zr_0·4O₃ ceramic has been prepared through solid state reaction route. X-ray diffraction shows that the sample has cubic perovskite structure with space group Pm-3m at room temperature. Temperature dependent dielectric study of the ceramic has been investigated in the frequency range 50 Hz-1 MHz. The density of the sample is determined using Archimedes’ principle and is found to be ∼99% of X-ray density. The dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behaviour in the ceramics. The index of relaxation (γ) and the broadening parameter (Δ) were estimated from a linear fit of the modified Curie-Weiss law. The value of γ ∼ 1·72 indicates the strong relaxor nature of the ceramic. A remarkably good fit to the Vogel-Fulcher relation further supports such a relaxor nature.     

Electrical conduction and thermal properties of Bi-doped Pr0·7Sr0·3MnO3 manganite

Electrical and thermal properties of Bi-doped Pr _0·7 Sr _0·3 MnO ₃ (PSMO) compounds are reported here. It is observed that Bi-doped PSMO compounds follow variable range conduction mechanism. Specific heat, thermal conductivity and thermo-power measurements show that larger Bi-ion, in place of smaller Pr ion, enhances their transition temperatures (T _MI, T _C, T _CP). Thermo-power measurements further strengthen our conclusion for the presence of magnetic polaron, generated due to hybridization of Bi ³⁺ –6s ² and O ^2? –2p orbital and polaronic conduction mechanism.     

Magneto-dielectric effect in Pb(Zr0·52Ti0·48)O3 filled nanoporous Ni 0 ·5Zn 0 ·5Fe 2 O 4 composite

Nanoporous Ni_0·5Zn_0·5Fe₂O₄ particles of diameter, ~ 9·5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m² g^???1 and the average pore diameter was 2·5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr_0·52Ti_0·48)O₃ was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2·4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni_0·5Zn_0·5Fe₂O₄ which exerted a compressive strain on Pb(Zr_0·52Ti_0·48)O₃ thereby lowering the tetragonality in its crystal structure.     

Wear perfornance of 0·6%Cr alloyed cast and heat treated steels with carbon contents of 0·7, 1·0, and 1·3%

Abstract

The effect of carbon content and heat treatment on the abrasive wear performance of three 0·6%Cr alloyed cast steels with carbon contents near the eutectoid composition (0·7, 1·0 and, 1·3%) were investigated using a pin on drum abrasion tester. Specimens were austenitised at 870,970, or 1070°C for 1 h and quenched. Additionally, a 1·3%C specimen was spheroidised, then austenitised at 870°C and quenched. The microstructure, which was dependent on heat treatment and carbon content, significantly influenced the wear rate. The wear rate is related non-linearly to hardness. The lowest wear rate was obtained for the 1·3%C alloy austenitised at 1070°C producing a quenched microstructure of 40% retained austenite and 60% martensite. This specimen also exhibited the lowest quenched hardness. However, for a practical industrial heat treatment, the 1·0 %C alloy austenitised at 970°C provides the best wear performance.

MST/3130     

Preparation and electrochemical properties of SrCe 0·4 Zr 0·4 Yb 0·2 O 2·9 electrolyte

The perovskite Yb-doped strontium cerate–zirconate material, SrCe_0·4Zr_0·4Yb_0·2O_2·9, was prepared by solid-state reaction and the structure was characterized by X-ray diffraction. The calcination process of the powder was investigated by thermogravimetric/differential thermal analysis (TG–DTA). The high temperature conductivities were measured by d.c. four-probe technique in the temperature range from 500 to 950°C in wet hydrogen and effect of temperature on conductivity was investigated. The conductivity increased with the elevation of temperature from 500 to 950°C. The highest conductivity of 4·4 × 10^???2 S· cm^???1 was observed for SrCe_0·4Zr_0·4Yb_0·2O_2·9 at 950°C. The current–voltage (I–V) and current–power (I–P) characteristics of the single cell (H₂, Pt/SrCe_0·4Zr_0·4Yb_0·2O_2·9/Pt, O₂) at temperature range from 600 to 850°C were tested. With the temperature increasing from 600 to 850°C, the open circuit voltage (OCV) decreased from 1·164 to 1·073 V and the ionic transfer number decreased from 0·996 to 0·946. At 850°C, the maximum power density of 25·2 mW· cm^???2 was observed.     

Rietveld analysis, dielectric and impedance behaviour of Mn3+/Fe3+ ion-modified Pb(Zr0·65Ti0·35)O3 perovskite

The polycrystalline samples of Pb(Zr_0·65???x A _x Ti_0·35)O₃ (A = Mn/Fe), (x =0·00, 0·05) (PZM/FT) were synthesized by conventional solid-state reaction technique. X-ray diffraction (XRD) pattern was recorded at room temperature and the samples were found in single phase form. All the observed peaks could be indexed to R3c space group with rhombohedral symmetry. XRD pattern has been analysed by employing Rietveld method with the help of FullProf Program. The lattice parameters and unit cell volumes decrease from Mn^3?+? to Fe^3?+? ion concentrations. The bond lengths and angles have been calculated by using Powder Cell Programme. Microstructural analysis of the surface of the ceramic compound by scanning electron microscopy (SEM) exhibits that there is a significant change in grain size on introduction of Mn^3?+? and Fe^3?+? ions at the Zr-site of the compound. It is observed that both the substitutions (Mn^3?+? and Fe^3?+?) at Zr site induce an increase in dielectric constant and a shift in Curie temperature (T _c ). From a.c. conductivity analysis, we have estimated the activation energy for both ferroelectric and paraelectric regions. Both the modified samples are obeying Jonscher power law. From Nyquist plots, the activation energy of grain resistance, relaxation time and bulk conductivity are compared. The grain resistance of the material decreases with rise in temperature which indicates a semiconducting behaviour of the material.     

Hot pressing effect on (Bi0·25Sb0·75)2Te3 mechanical and thermoelectric properties

(Bi_0·25Sb_0·75)₂Te₃ thermoelectric material is a well known p type of compound that has higher figure of merit than other stoichiometries. The crystal of this compound was prepared, pulverized in a particle size ratio of 64% with a mesh of 80 (200 μm²) and 36% with a mesh of 60 (250 μm²). The powder was sintered in a heat up to 350–500°C under pressure of 500 MPa (hot pressing). To find out the temperature effects on thermal conductivity of the sample it was systematically investigated in nano-scale intrinsic structures by systems of X-ray diffraction, scanning electron microscopy and, for only once successful attempt, atomic force microscopy. The acquired images ensured to show homogeneous structures for hot pressed samples. In terms of thermal conductivity and with regard to the figure of merit (Z), optimum sintering temperature hovers at around 500°C, which leads to a maximum Z value of around 1·53 K^?1.     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

Evidence for high ionic conductivity in lithium–lanthanum titanate, Li0·29La0·57TiO3

Lithium–lanthanum titanate, Li_0·29La_0·57TiO₃, is prepared by solid-state reaction method and it is furnace-cooled to room temperature. X-ray diffraction results indicated that the compound has tetragonal perovskite-like structure and the lattice parameters are determined as a = 3· 8714 Å and c = 7· 7370 Å. The average grain size is found to be 5 μm from SEM micrograph. The analysis of FTIR and Raman spectra of the sample supported tetragonal structure inferred from XRD data. The impedance spectrum of the sample is separated into bulk and grain boundary parts by analysing the impedance data. The high bulk ionic conductivity is reported as 1· 12 × 10^???3 S cm^?1 at room temperature. D.C. conductivity measurements indicate that the compound is a good ionic conductor.     

Spin canting phenomenon in cadmium doped cobalt ferrites, CoCd x Fe2−x O 4 ( x = 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), synthesized using sol–gel auto combustion method

Synthesis of non-collinear (spin canted) ferrites having the formula, CoCd _x Fe_2???x O ₄ (x?= 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), has been carried out using the sol–gel auto combustion method. The ferrite samples show an interesting magnetic transition from Neel to Yafet–Kittel configuration, as the Cd^2?+? concentration is increased beyond x?= 0·4. The FT–IR spectra confirm the formation of the metal oxide bond as they exhibit two frequency bands in the range of ~595 cm^???1 and ~450 cm^???1, corresponding to the tetrahedral and the octahedral stretching vibrations of the metal oxide, respectively. The structural evolutions of the nanophase investigated using powder X-ray diffraction (XRD) technique show that the average crystallite size is ~ 35 nm. The magnetic studies reveal that the saturation magnetization, M _s , increases up to x?= 0·4 and decreases when the value of x is >0·4. It is proposed that the incorporation of Cd^2?+? ion takes place into the tetrahedral sites and up to x?= 0·4, Neel’s model is followed. But for x?> 0·4, canting of spins occurs, as explained by Yafet–Kittel (Y–K) model. The d.c. resistivity decreases as a function of temperature, indicating semiconducting nature of the ferrites and the positive value of Seebeck coefficient establishes p-type conduction behaviour for all the ferrite samples.     

Microstructural and compositional modification of In0·53Ga0·47As/In0·52Al0·48As multiquantum wells using rapid thermal annealing process

Abstract

Quantum well intermixing of In_0·53Ga_0·47As/In_0·52Al_0·48As multiquantum wells (MQWs) in an impurity free vacancy diffusion (IFVD) mechanism was investigated to observe the intermixing aspect and the effect of defects in MQWs with regard to the microstructural aspect using transmission electron microscopy. The MQWs were grown on a GaAs (100) substrate using compositionally graded buffer layers via molecular beam epitaxy, and the MQWs were annealed at 750 and 900°C for 30 s via rapid thermal annealing for quantum well intermixing using IFVD method. In the fabricated MQWs, defects, such as stacking faults, twins and dislocations, were not generated at 750°C. The diffusion of Ga in the well layer for the quantum well intermixing started from the top well layer, because the SiO₂ layer that supplied vacancies for the quantum well intermixing was at the top of the sample. Additionally, in the same well layer, the intermixing did not show equality, because these vacancies were not supplied homogeneously. Especially, in the 900°C annealed case, many dislocations were generated from the cladding layer. These dislocations contributed to new vacancy generation sites, thus the quantum well intermixing was accelerated.     

Electrical properties of Sr x Ba1 − x Fe 0·6 Sn 0·4 O3 − ε NTC thermistors

Polycrystalline thermistor ceramics with the stoichiometric formula, Sr _x Ba_1???x Fe_0·6Sn_0·4O_3???ε (0·2 ≤ x ≤ 0·8), had been prepared by a standard solid state reaction route. X-ray diffraction analysis indicates that the ceramic system remains cubic perovskite structure with a very small lattice change. The electrical properties of Sr _x Ba_1???x Fe_0·6Sn_0·4O_3???ε thermistors were studied using a digital thermometer over a wide range of 298–400 K. The thermistors showed an excellent negative temperature coefficient (NTC) thermistor behaviour. The values of resistivity at 298 K (ρ ₂₉₈), thermistor constant (B _298/358) and activation energy (E _a) of the Sr _x Ba_1???x Fe_0·6Sn_0·4O_3???ε thermistors, decreasing with the increase of Sr content, were in the range of 0·37–11·0 kΩ ·cm, 2466–3703 K and 0·212–0·319 eV, respectively. For the thermistors with the compositions x?= 0·2 and 0·4, the fitting equivalent circuit was composed of three RCPE elements corresponding to grain, grain boundary and ceramic–electrode interface, respectively. From the impedance plots, it was found that the fitting data showed good agreement with the experimental data. The extracted grain boundary resistance exhibited a NTC thermistor behaviour.     

Technical note Modification of cast structure in Al–8·3Fe–0·8V–0·9Si alloy by magnesium treatment

Abstract

Chill cast Al–8·3Fe–0·8V–0·9Si alloy shows massive precipitate particles of various morphologies. The morphology, size, and distribution of those precipitates can be considerably modified by Mg treatment. A residual Mg level of about 0·2 wt-% is required for effective modification. Magnesium can be conveniently introduced into a superheated Al–Fe–V–Si alloy melt as either Al–20Mg or Ni–20Mg master alloy. Analysis by EDX of the complex aluminide and silicide precipitates have confirmed that Mg and Ni enter into the lattice of such precipitates.     

Decarburization in 0·5Cr–0·5Mo–0·25V steel and its effects on creep and microstructure

Abstract

Many high–temperature creep tests are performed on low–chromium, ferritic steels in an uncontrolled atmosphere. Examination of creep rupture specimens of 0·5Cr–0·5Mo–0·25V steel tested in air has shown that decarburization accompanies oxidation and is an important factor in accelerating the failure of creep tests in air. Similarly, pre-aging in air reduces the creep life more than pre-aging in a capsule. There is also evidence that decarburization is accelerated during straining. Measurements of surface carbon contents in 10 mm thick blocks heat treated in air at 600–700°C have given an apparent activation energy for decarburization of about 250 kJ mol^?1, at least twice that for carbon diffusing in ferrite. However, this value is still below that for creep, so the influence of decarburization on creep life is expected to increase at lower temperatures. Structural observations are discussed in relation to loss of carbon and are related to creep behaviour. Secondary precipitation was observed after low-temperature treatments in aged encapsulated specimens, but not in specimens aged in air. This is attributed to the loss of carbon in the air aged specimens, which also showed a decrease in the M₃C content. The iron content of M₃C particles depends on carbon content as well as aging time.

MST/40     

Electrical conductivity and chemical stability of BaCe0·8 − x A x Gd0·2O3 − δ (A = In, Zr, Ta; x = 0, 0·1) ceramics

BaCe_0·8???x A _x Gd_0·2O_3???δ (A = In, Zr, Ta; x?=?0, 0·1) ceramics were synthesized by solid-state reaction method. Microstructure and electrical properties of BaCe_0·8???x A _x Gd_0·2O_3???δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 573–1073 K in different atmospheres. BaCe_0·8Gd_0·2O_3???δ , BaCe_0·7In_0·1Gd_0·2O_3???δ and BaCe_0·7Zr_0·1Gd_0·2O_3???δ ceramics exhibit a single cubic perovskite structure. BaCe_0·7In_0·1Gd_0·2O_3???δ ceramic has the highest conductivity of 4·6 × 10^???2 S·cm^???1 in air at 1073 K. BaCe_0·7In_0·1Gd_0·2O_3???δ and BaCe_0·7Zr_0·1Gd_0·2O_3???δ ceramics exhibit an excellent chemical stability against boiling water. Indium is a suitable doping element to promote the sintering densification and to enhance both electrical conductivity and chemical stability of Gd-doped BaCeO₃ at operating temperatures.     

In situ templating synthesis of conic Ba0·5Sr0·5Co0·8Fe0·2O3?δ perovskite at elevated temperature

Conic Ba_0·5Sr_0·5Co_0·8Fe_0·2O_3−δ (BSCF) functional composite oxide was synthesized via a simple in situ templating process. The treatment of the solid precursor with concentrated nitric acid resulted in the mismatch of ionic radius at A-site and B-site of the ABO₃ perovskite, due to the oxidation of cobalt/iron ions, and the formation of Ba_0·5Sr_0·5(NO₃)₂ solid solution. Therefore, instead of the direct formation of BSCF oxide, an intermediate phase of Ba_0·5Sr_0·5CoO₃ (BSC) in hexagonal lattice structure and with conic particle shape was preferentially formed during calcination at low temperature. BSCF perovskite was then produced by the in situ templating of BSC with iron diffusing into the BSC lattice during calcination at high temperature. Well-crystallized BSCF particles in conic shape were obtained by the calcination of the nitric acid treated precursor at 900°C.     

Mn valence state and electrode performance of perovskite-type cathode La0·8Sr0·2Mn1 − x Cu x O3 − δ (x = 0, 0·2) for intermediate-temperature solid oxide fuel cells

Cu-free and Cu-doped LSM system, La_0·8Sr_0·2Mn_1???x Cu _x O_3???δ (x?=?0, 0·2), with perovskite structure were prepared using an EDTA combined citrate process and the effects of Cu ion at B-site were investigated. Electrical conductivity and polarization resistance of the Cu-doped LSM were 210 S·cm^???1 at 750 °C, and 2·54 Ω · cm² at 800 °C, respectively which were better than those of the Cu-free LSM. This indicated that the electrode performance of LSM was improved by the addition of Cu. The oxidation state of Mn ions increased with addition of Cu. The increase in the oxidation state of Mn ions was due to the formation of Mn^4?+? ions and oxygen vacancies. The addition of Cu ions to LSM systems could lead to enhanced electrode performance for oxygen reduction reactions originating from the change in valence of Mn ions.     

Preparation, characterization and luminescent properties of europium oxide doped nano LaMn0·9Zn0·1O3+d by sol-gel processing

New compounds of rare earth complex oxides with perovskite structure in a combination of La with Eu ions and Mn with Zn ions, La_1−x Eu _x Mn_0·9Zn_0·1O_3+d (LEMZ) (0·0 ≤ x ≤ 0·32) in A and B sites, respectively were synthesized. X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and photoluminescence spectra (PL) were used to characterize the resulting nanoparticles. The powder X-ray diffraction peaks could be indexed as a rhombohedral cell. The results of FT-IR spectra were in agreement with those of XRD. High-quality nanopowders with controlled stoichiometry and microstructure were prepared at a temperature range of 700–800°C for 6 h, with mean particle sizes of ∼ 17·5 nm. Photoluminescence measurements showed Eu³⁺ ions characteristic red emission in crystalline LEMZ powders due to the ⁵ D ₀ → ⁷ F _J (J = 0–6) transitions of the 4f electrons of Eu³⁺ ions. The structure, homogeneity and particle size of the obtained compounds during different stages were investigated by scanning electron microscopy (SEM).     

Relaxation effect of pulse current on Ti50·0Ni50·0 structure during rolling

Abstract

Using transmission electron microscopy and differential scanning calorimetry, the microstructure and martensitic transformation of the Ti_50·0Ni_50·0 alloy after cold rolling and after rolling with a pulse current were compared. A structural relaxation effect was observed in the alloy during rolling with current. The effect is manifested in the more slow kinetics of the structure formation and less intensive suppression of martensitic transformations at rolling with current compared to cold rolling with some deformation degrees.     

0～3mm双面百分表

一、引言我厂生产的 0～ 3ｍｍ双面百分表是根据用户的使用要求在我厂原有 0～ 3ｍｍ百分表的基础上改造设计而成的 ,它除了具有 0～ 3ｍｍ百分表的使用功能以外 ,还具有一次装夹 ,两面读数的功能 ,适用于单面百分表不便使用的场合 ,主要用作检测装置的读数头。二、外部型式和尺寸双面百分表的型式和尺寸如图 1所示。三、结构和工作原理双面百分表的结构简图如图 2所示 ,工作原理是当给测头一个位移信号时 ,测头带动量杆上齿条的移动 ,由于齿条与高轮啮合带动铜齿轮的转动 ,铜齿轮又与中心齿轮啮合带动中心齿轮的转动 ,由于主指针安装在中心…