Small Amount Of Second Phase Research Articles

Impedance spectroscopy and piezoresponse force microscopy analysis of lead-free (1 − x) K0.5Na0.5NbO3 − xLiNbO3 ceramics

(1 − x) K0.5Na0.5NbO3 − xLiNbO3 (where x = 0.0, 5.0, 5.5, 6.0, and 6.5 wt.%) (KNLN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phase was formed for pure KNN while a small amount of second phase (K6Li4Nb10O30, ∼3%) was present in LN doped KNN ceramics. Phase analysis indicated the change in the crystal structure from orthorhombic to tetragonal with increase in LN content. The electrical behavior of the ceramics was studied by impedance spectroscopy technique in the high temperature range. Impedance analysis was performed using an equivalent circuit model. The impedance response in pure KNN and KNLN ceramics could be deconvoluted into two contributions, associated with the bulk (grains) and the grain boundaries. Activation energies for conductivity were found to be strongly frequency dependent. The activation energy obtained from dielectric relaxation data was attributed to oxygen vacancies. From PFM we found that the composition with 6.5 wt.% LN displays stronger piezocontrast as compared to pure KNN implying an evidence of a pronounced piezoelectric coefficient.

Synthesis of La0.85Sr0.15Ga0.8Mg0.2O3 − δ powder by carbonate co-precipitation combining with azeotropic-distillation process

La0.85Sr0.15Ga0.8Mg0.2O3−δ (LSGM1520) powder is synthesized by a carbonate co-precipitation coupling with azeotropic-distillation process. The composition of the as-prepared precipitate is determined by X-ray diffraction (XRD), elemental analysis (EA), thermogravimetric and differential scanning calorimeter (TG-DSC) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The post-distilled precursor is submitted to various thermal treatments and characterized by XRD and transmission electron microscopy (TEM). The results show that the components of the powder calcined at 1000°C contain a main perovskite phase and small amounts of secondary phases (namely LaSrGaO4 and LaSrGa3O7). TEM observation reveals that the powder has a narrow grain size distribution, which turns out to be suitable for sintering (>97% relative density for a pellet sintered at 1400°C during 4h). The conductivity of sintered pellets is measured and the highest conductivity at 800°C of LSGM1520 is 0.186Scm−1, which is nearly three times as high as that of La0.8Sr0.2Ga0.8Mg0.2O3−δ (0.0644Scm−1) prepared by the similar carbonate method. It suggests that a new route of synthesizing Sr- and Mg-doped lanthanum gallate (LSGM) with good sinterability has been developed.

Improvement of thermoelectric performances of Bi2Sr2Co1.8Ox textured materials by Pb addition using a polymer solution method

Bi1.6Pb0.4Sr2Co1.8Ox ceramics have been prepared through a polymer solution method using polyethyleneimine. From these powders, bulk textured materials have been prepared using a melt growth technique. Microstructure has been observed by scanning electronic microscopy (SEM) which has shown that samples are mainly composed by the thermoelectric phase, with small amounts of secondary phases. Electrical resistivity measurements showed very small values nearly constant with temperature, whilst thermopower increases from room temperature to 650°C. Power factor at 50°C is about 0.15mW/K2·m and 0.30 at 650°C, which makes these ceramics good candidates for power generation applications.

Preparation of Single Phase Bismuth Niobium Based Perovskite-type Oxides

Due to an environmental concern, a lead-free ferroelectric with properties comparable to those of lead zirconate titanate is required. Based on the tolerance factor, the single perovskite phase of Bi1/2K1/2(X1/3Nb2/3)O3 (X = Cu BKCuN, X = Mg BKMgN or X = Zn BKZnN). The X-ray diffraction (XRD) patterns showed that all the samples sintered largely consisted of the perovskite phase, with small amounts of second phases. By adding BaTiO3, these ceramics were observed perovskite single phase. Those electric properties were investigated.

Yttrium-doped effect on thermoelectric properties of La0.1Sr0.9TiO3 ceramics

Ceramic samples of La0.1YxSr0.9–xTiO3 with different yttrium concentration have been synthesized by conventional solid state reaction technique, and their thermoelectric properties have been investigated. X-ray diffraction characterization confirms that the main crystal structure is of perovskite, but with a small amount of second phase of Y2Ti2O7 for samples with x = 0.05, 0.08, and 0.10. SEM images indicate all ceramic samples are dense and compact, and the largest grain size appears in sample with x = 0.03 and 0.05. Also the second phase can also be identified from the SEM images for x = 0.05, 0.08, and 0.10 samples. Electrical conductivity and Seebeck coefficient of samples have been measured in the temperature range between 300 and 1100 K. With increasing of yttrium concentration, electrical resistivity decreases, and reaches 0.8 mΩ cm for x = 0.10 sample at room temperature. The absolute Seebeck coefficients increase monotonically with increasing temperature in the whole temperature range. Sample with x = 0.03 exhibits the highest absolute Seebeck coefficient 219 μV K−1 at 1059 K, as well as the maximum power factor 11 μW cm−1 K−2 at 624 K.

Enhanced oxygen reduction activity on surface-decorated perovskite thin films for solid oxide fuel cells

Surface-decoration of perovskites can strongly affect the oxygen reduction activity, and therefore is a new and promising approach to improve SOFC cathode materials. In this study, we demonstrate that a small amount of secondary phase on a (001) La0.8Sr0.2CoO3−δ (LSC) surface can either significantly activate or passivate the electrode. LSC (001) microelectrodes prepared by pulsed laser deposition on a (001)-oriented yttria-stabilized zirconia (YSZ) substrate were decorated with La-, Co-, and Sr-(hydr)oxides/carbonates. “Sr”-decoration with nanoparticle coverage in the range from 50% to 80% of the LSC surface enhanced the surface exchange coefficient, kq, by an order of magnitude while “La”-decoration and “Co”-decoration led to no change and reduction in kq, respectively. Although the physical origin for the enhancement is not fully understood, results from atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy suggest that the observed kq enhancement for “Sr”-decorated surfaces can be attributed largely to catalytically active interface regions between surface Sr-enriched particles and the LSC surface.

Synthesis and dielectric characterization of Ba 0.6Sr 0.4TiO 3 ferroelectric ceramics

Ferroelectric ceramics Ba 0.6Sr 0.4TiO 3 (BST 40) were prepared, by solid-state reaction in the temperature range 1210–1450 °C. Maximum values of the ceramic densities were around 94% of their theoretical value. X-ray diffraction techniques (XRD) and scanning electron spectroscopy (SEM) were used to analyze the structure and the surface morphology of ceramics. Rounded, well defined or abnormal granular growth was observed in the SEM images, vs. sintering conditions and purity of the raw materials. In all samples, BST 40 ceramic is the major phase, but there are also present small amounts of secondary phases, as revealed in XRD diffraction patterns. Permittivity and dielectric loss measurements were performed in the temperature range − 150 to + 150 °C, and 150 Hz–5 MHz frequency values. Permittivity values rising from 1200 to 12,500, with increasing sintering temperatures, were recorded. Narrow and well defined transition peaks were noticed at higher sintering temperatures. Curie temperature was around 2 °C, for samples with the mentioned composition. Permittivity and losses vs. frequency show different behavior whether BST ceramics are in polar or non-polar state and with the distance toward phase transition. Microwave measurements performed at room temperature have shown lower values of permittivity, compared with similar data at low frequency, and dielectric losses lower than 1% at 0.7 GHz. The sintering conditions (temperatures, sintering time, etc.) and purity of the raw materials lead to important changes of transition temperatures in the polymorphic diagram, which we have built—for the other Ba1−xSrxTiO3 compositions (x = 0.25–0.90) sintered at 1260 °C for 2 h.

Plasma-Sprayed Strontium- and Magnesium-Doped Lanthanum Gallate Ceramics

La1−xSrxGa1−yMgyO3−d (LSGM) powder of different composition and a grain size of about 5–10 μm were plasma sprayed on Ti substrates in order to study the effect of plasma spraying of LSGM on the microstructure and chemical composition of the resulting ceramic LSGM layers. As-sprayed LSGM layers contain a considerable amount of amorphous phase besides LSGM grains, whereas postannealed layers mainly consist of LSGM besides very small amounts of second phases. Evaporation of mainly Ga was observed, which considerably altered the chemical composition of the layers.

Structural, magnetic and dielectric properties of Bi1−ySryFe(1−y)(1−x)Sc(1−y)xTiyO3 (x=0–0.2, y=0.1–0.3) ceramics

Bi 1− y Sr y Fe (1− y )(1− x ) Sc (1− y ) x Ti y O 3 ( x = 0–0.2, y = 0.1–0.3) ceramics were obtained by solid-state reaction method. Addition of scandium could simultaneously reduce magnetic coercive field and enhance dielectric properties of prepared samples. ▶ The electrical resistivity of BiFeO 3 is enhanced by forming solid solution with SrTiO 3 . ▶ We further replace Fe 3+ by Sc 3+ in solid solution to reduce H c and achieve a soft magnet. ▶ Structure–magnetic property relationship has been established by Rietveld refinement . ▶ Sc 3+ substitution can inhibit the dielectric loss effectively. In this study, bulk ceramics with general formula Bi 1− y Sr y Fe (1− y )(1− x ) Sc (1− y ) x Ti y O 3 ( x = 0–0.2, y = 0.1–0.3 mol%) were prepared by traditional solid-state reaction method. As a comparison, bulk BiFeO 3 (BF) was also sintered by rapid sintering method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that apart from a small amount of secondary phase detected in BF, all other samples crystallized in pure perovskite structure and maintained original R3c space group. The room temperature M – H curves were obtained. While BF had a coercive magnetic field ( H c ) of 150 Oe, Bi 1− y Sr y Fe 1− y Ti y O 3 solid solutions had a much larger value (for y = 0.1, 0.2, 0.3, H c were 4537, 5230 and 3578 Oe, respectively). Sc 3+ substitution decreased the H c values of these solid solutions remarkably, and resulted in soft magnetic properties, as well as a decrease of the dielectric loss. At 1 MHz, the tan δ of Bi 0.7 Sr 0.3 Fe 0.7(1− x ) Sc 0.7 x Ti 0.3 O 3 with x = 0.05, 0.1, 0.15, 0.2 were 0.1545, 0.1078, 0.1046 and 0.1701, respectively.

New solution method to produce high performance thermoelectric ceramics: A case study of Bi-Sr-Co-O

Bi 2Sr 2Co 1.8O x ceramics have been synthesized through a solution method involving the addition of polyethyleneimine as coordinating agent for the metallic cations. From these powders, bulk sintered materials have been prepared. Microstructure has been studied by means of scanning electronic microscopy (SEM) and it has shown that samples are mainly composed by the thermoelectric phase, with very small amounts of secondary phases. Electrical resistivity measurements showed very small values (around 21 mΩ cm at room temperature), nearly constant with temperature, while thermopower increases rapidly to values higher than 200 μV/K at 650 °C. Power factor value at 50 °C is about 0.08 mW/K 2 m and 0.20 at 650 °C, which makes this ceramic a potential material for power generation applications.

La0.8Sr0.2Ga0.8Fe0.2O3−δ: Influence of the preparation procedure on reactivity toward methanol and ethanol

In this paper a strontium- and iron-doped lanthanum gallate (La0.8Sr0.2Ga0.8Fe0.2O3—LSGF) is prepared by Pechini process and polyacrylamide gel method. The powders are characterized by means of X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT), Thermal Programmed Desorption (TPD), Thermal Programmed Reduction (TPR), BET specific surface area, UV–Vis and Mössbauer Spectroscopy (MS). The activity toward methanol and ethanol is investigated by Infrared (IR) spectroscopy and Quadrupolar Mass Spectrometry (QMS) under several conditions. XRD outcomes reveal the formation of the desired perovskite phase at 900°C, however, small amounts of secondary phases are also present. LSGF synthesized by Pechini process is characterized by a lower amount of secondary phases. On the other hand, LSGF from polyacrylamide gel method has a higher specific surface area. XPS data show that the two samples differ for surface cations segregation, hydroxylation degree and carbonate contamination. These results are also confirmed by DRIFT and TPD measurements. MS and TPR analyses reveal the presence of a small amount of Fe(IV), which is reduced to Fe(III) with H2 (5% in Ar) at about 450°C and with CH3OH vapours at 200°C. Catalytic tests prove that methanol is mainly decomposed into H2 and CO at 400°C, but small amounts of CO2 are also detected. Ethanol undergoes essentially dehydrogenation thus forming acetaldehyde and H2. In oxidizing conditions, both alcohols are oxidized to CO2 and H2O at 400°C, nevertheless, partially oxidized products are also observed. Acetaldehyde is an important product in ethanol oxidation. Under steam reforming conditions, methanol and ethanol give H2, CO and CO2, but acetaldehyde is also observed in ethanol steam reforming. The presence of acetaldehyde, when dealing with ethanol, suggests a difficult C–C bond break. Both the LSGF samples undergo poisoning during the reactions.

Effect of non-stoichiometry on hydrogen storage properties of La(Ni 3.8Al 1.0Mn 0.2) x alloys

The La(Ni 3.8Al 1.0Mn 0.2) x ( x = 0.94, 0.96, 0.98, 1.0) hydrogen storage alloys have been investigated to examine the effect of non-stoichiometry on the crystal structure, activation performance, hydrogen absorption/desorption properties and cycle life. It was found that for the stoichiometric compound, only single phase with CaCu 5 type structure exists. However, for B-poor compounds of AB 5 alloys, there is a principal CaCu 5 type phase with a small amount of second phase and the amount of second phase increased with decreasing x when x ≥ 0.96 and reached a maximum when x = 0.96. The activation becomes harder with decreasing x until x = 0.96 and easier when x decreased to 0.94. The plateau pressure increased and the hydrogen uptake capacity decreased with decreasing x when x ≥ 0.96, and then decreased and increased, respectively, when x further decreased to 0.94. Both the change in the lattice strain which could be estimated by FWHM (full width at half maximum) and the degree of slope factor S f in the alloys show the same trend with the change of x, exhibiting a maximum at x = 0.96. The Δ H decreased with decreasing x when x ≥ 0.96 and then increased when x = 0.94 and it was found that the larger the cell volume, the larger the absolute value of the enthalpy. The pulverization resistance of the alloys was greatly improved by the non-stoichiometric. The kinetics of the alloys was very fast and almost not influenced by the change of non-stoichiometric x. After 300 absorption/desorption cycles, the hydrogen uptake capacity of the stoichiometric and non-stoichiometric alloys almost kept the same, but the particle size decreased greatly.

STRUCTURE AND MAGNETIC PROPERTIES OF TB0.27 DY0.73FE1.9+xTI0.05 COMPOUNDS

Structure, Curie temperature, and magnetostriction have been systemically investigated for Tb 0.27 Dy 0.73 Fe 1.9+x Ti 0.05 compounds using X-ray diffraction, vibrating sample magnetometer, and standard strain gauge technique. The samples show pure MgCu 2-type Laves phase when x≥0.2, and a small amount of second phases appear when x>0.2. The lattice parameters and the Curie temperatures change modestly with increasing Fe content. The magnetostriction of Tb 0.27 Dy 0.73 Fe 1.9+x Ti 0.05 compounds shows strong dependence on Fe content.

Carbonate coprecipitation synthesis of Sr- and Mg-doped LaGaO 3

A carbonate coprecipitation synthesis, simple and easily scalable to industrial level, has been successfully applied to produce Sr- and Mg-doped LaGaO 3. The thermal evolution shows that the main perovskite phase crystallizes already at 1000 °C. Samples sintered at 1400 °C for 10 h have a relative density of 93% and an electrical conductivity of 7.7 ∙ 10 − 2 S cm − 1 at 800 °C, similar to the one reported for solid state synthesis. The presence of small amounts of secondary phases (about 17%) such as LaSrGaO 4 and LaSrGa 3O 7 does not seem to deeply affect the electrical properties of the final material.

Effects of nano-carbon doping and sintering temperature on microstructure and properties of MgB 2

We fabricated nano-carbon (NC) doped MgB 2 bulks using an in situ process in order to improve the critical current density ( J c) under a high magnetic field and evaluated the correlated effects of the doped carbon content and sintering temperature on the phase formation, microstructure and critical properties. MgB 2− x C x bulks with x = 0 and 0.05 were fabricated by pressing the powder into pellets and sintering at 800 °C, 900 °C, or 1000 °C for 30 min. We observed that NC was an effective dopant for MgB 2 and that part of it was incorporated into the MgB 2 while the other part remained (undoped), which reduced the grain size. The actual C content was estimated to be 68–90% of the nominal content. The NC doped samples exhibited lower T c values and better J c(B) behavior than the undoped samples. The doped sample sintered at 900 °C showed the highest J c value due to its high doping level, small amount of second phase, and fine grains. On the other hand, the J c was decreased at a sintering temperature of 1000 °C as a result of the formation of MgB 4 phase.

Microstructure, surface composition and chemical stability of partly ordered LaTiO 2N

LaTiO 2N was synthesized in a thermal ammonolysis process of crystalline La 2Ti 2O 7 prepared by conventional solid state reaction or by ammonolysis of a homogeneous amorphous precursor obtained from a soft-chemistry approach. At room temperature slowly cooled LaTiO 2N prepared from either precursor crystallizes in space group I 1 ¯ and shows a partially ordered anionic arrangement, in contrast to a quenched reference sample. The material possesses a complex microstructure represented by twin domains of different types and orientations, as well as incommensurately modulated fragments. The presence of minor C- and N-containing phases such as carbonates, cyanides and nitrates as well as a small amount of a reoxidation intermediate was detected by infrared and Raman spectroscopy. These small amounts of secondary phases can generally influence the results of the O/N content determination of oxynitride compounds when using thermal analysis methods. The formation of such unwanted secondary phases can be avoided by quenching the oxynitride sample or by cooling in inert atmosphere.

Preparation and properties of the CoFe 2O 4–Nb–Pb(Zr,Ti)O 3 multiferroic composites prepared in situ by gel-combustion method

Di-phase magnetoelectric composites formed by magnetic CoFe 2O 4 and ferroelectric Nb–Pb(Zr,Ti)O 3 were prepared by citrate–nitrate combustion method technique by using Nb–Pb(Zr,Ti)O 3 template powders prepared by mixed oxides. Pure di-phase powder composites with a good crystallinity were obtained after the calcination step. The purity was maintained by sintering at temperature of 1100 °C/2 h, which ensured limited reactions at interfaces, while by sintering at 1250 °C/2 h, small amounts of secondary phases resulted. The method allowed to produce di-phase ceramics with homogeneous microstructures and a very good mixing of the two phases. The dielectric and magnetic investigations at room temperature confirmed the formation of composite ceramics with both dielectric and magnetic properties at room temperature, with permittivity and magnetization resulted as sum properties from the parent Pb(Zr,Ti)O 3 and ferrite phases.

In situ preparation of CoFe 2O 4–Pb(ZrTi)O 3 multiferroic composites by gel-combustion technique

Diphase magnetoelectric composites of CoFe 2O 4–Pb(ZrTi)O 3 were prepared by citrate–nitrate combustion technique by using Pb(Zr,Ti)O 3 template powders obtained by the mixed oxide method. Pure diphase powder composites with a good crystallinity were obtained after calcination. The composition and purity were maintained after sintering at temperature of 1100 °C/2 h, which ensured limited reactions at interfaces, while by sintering at 1250 °C/2 h, some small amounts of secondary phases identified as nonstoichiometric ZrO 2− x resulted. The method allowed to produce diphase ceramics with homogeneous microstructures and a very good mixing of the two phases. The dielectric and magnetic investigation at room temperature confirmed the formation of composite ceramics with both dielectric and magnetic properties at room temperature, with permittivity and magnetization resulted as sum properties from the parent Pb(Zr,Ti)O 3 and ferrite phases.

Effect of second phase on single phase flow meters in steam quality measurement

This paper presents results from an investigation of the two phase flow, especially liquid ingas phase, in most mainly used flow meter in steam industry namely differential pressuremeter is investigated. As in general, a flowmeter is designed and employed to measure flowrate of single phase fluid. There are many types of meter available in the market characterizeby their working principles, installed conditions and measured fluid. All meters representtheir accuracies under the single phase flow condition. However, when they are working inunusual conditions especially under multiphase flow, most meters lose their accuraciessignificantly even there is small amount of second phase introduced into the system. Tounderstand the deteriorated performance of the meter under two phase flow, additional studyon the effect the second phase on the meter is required.The laboratory experiment is set up to simulate the wet steam by flowing compressed airin the 2 inch pipe. Water droplet is generated by pressurized water flowing through a nozzleand then spayed into the system in range of 25% maximum by mass fraction. The signal fromeach flowmeter is collected by digital computer and analyzed using FFT and power spectrumdensity. The results show that the presence of the second phase in the system causes highfrequency fluctuation and causes significant error on meter reading. Flow manufacturersalways add low-pass filter circuit to remove this high frequency signal, however, this papershows that the high frequency signal in specific region is useful as it can be use to estimatedthe percentage of the second phase in the main phase system.

Thermoelectric Properties of Ca-Ir-O Compounds Prepared by Spark Plasma Sintering

Ca-Ir-O compounds in various molar ratios of Ir to Ca (RIr/Ca) from 0.2 to 1.2 were synthesized by solid-state reaction and compacted by spark plasma sintering (SPS). Ca4IrO6 and CaIrO3 with a small amount of second phase were obtained at RIr/Ca=0.25 and 1.0, respectively, whereas Ca2IrO4 in a single phase was obtained at RIr/Ca=0.5. The electrical conductivity was 4×10−4 to 150 Sm−1 at room temperature and exhibited a semiconducting behavior for all the samples. The Seebeck coefficient at RIr/Ca=0.4 to 0.7 showed negative values whereas samples with RIr/Ca=0.25 and 0.9 to 1.2 showed positive values. The thermal conductivity was 1.1 to 2.7 Wm−1K−1 at room temperature and slightly decreased with increasing temperature. The highest ZT value of p-type was 0.006 at 1023 K and RIr/Ca=1.1 and 1.2, while that of n-type was 0.0022 at 800 K and RIr/Ca=0.5.