Conventional Ceramic Method Research Articles

Microstructure and electrical properties of Sm2O3-doped ZnO-based linear resistance ceramics

ZnO-based linear resistance ceramics were synthesized from ZnO–MgO–NiO–Al2O3–SiO2–Sm2O3 at 1320 °C for 3 h by the conventional ceramics method. The microstructure and electrical properties of the linear resistance ceramics have been systematically investigated in detail. The experimental result indicates that appropriate amounts of Sm2O3 addition can obviously improve the resistance temperature coefficient of ZnO-based linear resistance ceramics compared with the Sm2O3-free samples. The samples with the Sm2O3 content of 0.5 mol% exhibit excellent electrical properties with the resistivity of 209.8 Ω cm and the resistance temperature coefficient of 2.38 × 10−4/°C, which is improved by 46 and 92 %, respectively. Moreover, the nonlinear coefficient of voltage decreases to 1.15, decreased by 4.30 % and the relative density reaches to 96.43 %, increased by 4.91 %.

Structural, Magnetic, and Electrical Study of Polycrystalline Pr0.55Sr0.45−x Na x MnO3 (x = 0.05 and 0.1)

Structural, magnetic, magnetocaloric, and electrical properties of Pr0.55Sr0.45−x Na x MnO3 (x = 0.05 and 0.1) have been investigated. Our samples were elaborated using the conventional ceramic method at high temperature. Rietveld refinement of the X-ray diffraction patterns shows that all our compounds are single phase and crystallize in the orthorhombic structure with Pbnm space group. Low field magnetic measurements indicate that all investigated samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. This transition takes place at room temperature. A large magnetocaloric effect has been observed in all our compounds. The maximum value of the magnetic entropy change is found to be 3.87 J K−1 kg−1 for the sample with x = 0.05 under 5T. The values of relative cooling power (RCP) are 246.52 J kg−1 for x = 0.05 and 262.73 J kg−1 for x = 0.1, respectively, for an applied magnetic field of 5T. The electrical resistivity measurements reveal a metal–semiconductor transition with increasing temperature with the presence of a resistivity minimum at low temperature which is attributed to the electron–electron columbic interactions.

Brillouin function characteristics for La-Co substituted barium hexaferrites

La-Co substituted barium hexaferrites with the chemical formula of Ba1−xLaxFe12−xCoxO19 (x = 0.0, 0.1, 0.3, and 0.5), prepared by a conventional ceramic method, were systematically investigated by Raman spectra, X-ray photoelectron spectroscopy, Rietveld refinement of X-ray diffraction patterns, and vibrating sample magnetometer. The result manifests that all the compounds are crystallized in magnetoplumbite hexagonal structure. Trivalent cobalt ions prevailingly occupy the 2a, 4f1, and 12k sites. According to Néel model of collinear-spin ferrimagnetism, the molecular-field coefficients ωbf2, ωkf1, ωaf1, ωkf2, and ωbk of La-Co substituted barium hexaferrites have been calculated using the nonlinear fitting method, and the magnetic moment of five sublattices (2a, 2b, 4f1, 4f2, and 12k) versus temperature T has been also investigated. The fitting results are coincided well with the experimental data. Moreover, with the increase of La-Co substitution amount x, the molecular-field coefficients ωbf2 and ωaf1 decrease constantly, while the molecular-field coefficients ωkf1, ωkf2, and ωbk show a slight change.

Synthesis and Investigation of the Structural Properties of Al<sup>3+</sup> Doped Mg Ferrites

The polycrystalline ferrites of MgAlxFe2-xO4 (0.0≤x≤0.4) were prepared by the conventional solid state ceramic method. The specimens were sintered at 13500C and X-ray diffraction experiments were done at room temperature which showed single phased cubic spinel structure. The lattice parameters were determined from the XRD data using Nelson-Riley extrapolation method and found to decrease with increasing Al concentration obeying Vegard’s law. The cation distribution and oxygen position parameters have also been determined by refining the data using the RIETAN-2000 in the Rietveld method which reveals that the samples possess cubic symmetry corresponding to the space group Fd-3m. The X-ray density and bulk density of each sample were calculated using the lattice parameters. The porosity has been determined from X-ray density (ρx) and bulk density (ρB) and it changes monotonically with Al content.

Study of the Dielectric Properties of Europium Doped Barium Titanate Ceramics by an Impedance Spectroscopy

The barium titanate (BaTiO3) and the BaTiO3 + 0.1wt.% Eu2O3 ceramics were prepared by a conventional ceramic method. The structural studies were carried out by means of an X-ray diffraction technique. The influence of the grains and the grain boundaries on the electrical properties was investigated using a impedance spectroscopy. This technique enables us to determine the values of grain and grain boundary resistance. The results show that the Eu doping leads to a significant reduction in the resistance value of the grains (˜105Ω) with respect to the pure BT ceramics (˜107Ω). The conductivity processes were determined from the Arrhenius behaviour of grain and grain boundary resistances.

Magnetic and magnetocaloric study of manganite compounds Pr0.5A0.05Sr0.45MnO3 (A=Na and K) and composite

Structural, magnetic and magnetocaloric properties of Pr0.5A0.05Sr0.45MnO3 (A=Na and K) have been investigated. Our samples have been elaborated by the conventional ceramic method at high temperature. X-ray diffraction patterns using Rietveld refinement reveal that our compounds are single phase and crystallize in the orthorhombic structure with Pbnm space group. Magnetization measurements versus temperature under an applied magnetic field of 50mT indicate that all our investigated samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The values of the Curie temperatures are 270K and 275K for A=Na and K, respectively. The magnetocaloric study of a manganite-based composite reveals an enhancement of relative cooling power which is around 67.37% of pure Gd under an applied magnetic field of 5T.

Effect of sintering aid ZnO–CeO2 on dielectric properties of (Zr0.8Sn0.2)TiO4 ceramics

(Zr0.8Sn0.2)TiO4 (ZST) ceramics were prepared by conventional solid-state ceramic method. The effects of ZnO + CeO2 on the phase composition, microstructure, sintering characteristics and microwave dielectric properties of ZST ceramics were investigated. Only a single phase (Zr0.8Sn0.2)TiO4 was identified for XRD patterns. The sintering temperature decreased from 1550 to 1220 °C owning to the composite addition of ZnO and CeO2. The excellent microwave dielectric properties have been obtained in the samples of ZnO (1 wt%) + CeO2 (0.5 wt%) doped ZST ceramics sintered at 1220 °C for 4 h: er = 37, Q × f = 33,000 GHz, τf = −0.76 ppm/°C.

Fabrication of Bimetallic (NiFe) Anode-Supported SOFCs with Direct Ceramic Inkjet Printing

Anode-supported solid oxide fuel cells (SOFCs) based on nickel-iron supports were fabricated, and their performance evaluated at the intermediate temperatures. The ratio of NiO to Fe2O3 in the metal support was 7 to 3 on a molar basis. Fe2O3 and NiO powders and appropriate sintering aids were mixed in the desired proportions and discs were die-pressed. The goal of using sintering aids was to adjust the thermal expansion of the support and the electrolyte to a close match within the sintering temperature region. The functional coatings were sequentially applied on the metal support by the use of Direct Ceramic Inkjet Printing (DCIJP) of suspension inks. The use of DCIJP enables the formation of very thin electrolyte coatings (~10µm), which is challenging for the more conventional ceramic methods. It also allowed infiltration of the support composites into the porous scaffolding of the support, thus extending the active anode area. The reduction of utilised and wasted amounts of active materials can lead to significant cost reductions in the fabrication of the final cell. Two distinct cell structures were produced - first one consisted of four distinct layers- metal support (NiFe), anode functional layer (Ni/GDC), electrolyte (10Sc1CeSZ) and cathode (LSCF+ GDC) and the second one where the anode deposition was omitted and the anode was formed by infiltration of ink directly into the NiFe support during the printing of the electrolyte. Cells were tested with hydrogen as fuel and air as oxidant at temperatures up to 750oC. XRD and SEM examination indicated that the good performance of the button cells can be ascribed to the optimized composition and microstructure of the anode. The present work shows that high performance FeNi based cells can be successfully fabricated by the sole use of ceramic technology - DCIJP. Figure 1

Enhanced Magnetization in Mg–Zn Ferrite Nanoparticles, Prepared by Mechanochemical Processing

One-step mechanochemical processing is one of the most useful and effective methods to produce nanoparticles. Prepared materials by this method show novel properties. In this work, Mg-substituted Zn ferrite (Mg x Zn1−x Fe2O4; x = 0.0, 0.2, 0.4, 0.6) nanoparticles were prepared by one-step mechanochemical processing for the first time. In addition, bulk samples with the same compositions were prepared by conventional ceramic method, which served as reference samples. The samples were characterized by the X-ray diffraction and field emission electron microscopy. By a comparison between I(220)/I(222) intensity ratios in X-ray diffraction patterns of the samples prepared by one-step mechanochemical processing and those of the bulk samples, changes in the cation distribution of the samples prepared by one-step mechanochemical processing were followed. Lattice parameters and magnetic properties of the all samples were measured, and their behaviors were discussed.

Relation between microstructures and electric properties for 3Y-TZP/Ba0.5Sr0.5Fe12O19 composites prepared by two different methods

Relation between microstructures and electric properties of 3-mol%-yttria-doped zirconia (3Y-TZP)/Ba0.5Sr0.5Fe12O19 composites prepared by two different methods were investigated. Ba0.5Sr0.5Fe12O19 ferrite powders were firstly prepared by solid reaction and sol–gel process, respectively. They were then combined with 3Y-TZP. Finally, the mixture powders were molded and sintered by a conventional ceramic method. The electric properties of the composites were studied through the impedance and dielectric spectroscopy. A corresponding equivalent-circuit model including the constant phase element of the composites was obtained using Zview software. The grain boundary morphology of the both composites was analyzed using fractal theory. A mathematical evaluation of the grain boundary morphology of the both composites can be given by the box-dimension. The information of the microstructure features of the composites can be indirectly reflected by the obtained parameters of the equivalent-circuit model and dielectric loss peak.

Dielectric and electrical properties of Cr substituted Mg ferrites

The spinel ferrites MgCrxFe2-xO4 (0.0 ? × ?1.0) were prepared through the solid state reaction using conventional ceramic method at 1300°C in air. The homogeneous phase of the ferrite samples was observed from the X-ray diffraction study. Lattice parameter of the samples was found to decrease with increasing Cr concentration in the system obeying Vegard’s law. The ac electrical resistivity, measured as a function of temperature, decreases with the increase of temperature indicating the semiconducting nature of all the samples. The activation energies were calculated and found to decrease with increasing Cr content. The lower activation energies are associated with higher electrical conductivity. With the increase of temperature, dielectric constant (e`) and dielectric loss tangent are observed to be increased; while with the increase of frequency, dielectric constant (e`) and dielectric loss tangent decrease for all the samples.Journal of Bangladesh Academy of Sciences, Vol. 39, No. 1, 1-12, 2015

Structural, Magnetic, and Electrical Properties of Ni0.65Zn0.35−x Cu x Fe2 O 4 Nanoferrite System

Copper-substituted Ni–Zn nanoferrite system having the composition of Ni0.65Zn0.35−xCuxFe2O4 (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) has been prepared by autocombustion method. Structural and magnetic characterizations were done on the as-prepared powders while the dc electrical conductivity measurements were studied on pellets sintered at 900 ∘C. X-ray diffraction measurements of all the samples showed a single spinel phase. The lattice parameter has been found to decrease with increasing Cu, and this variation in the spinel unit cell is ascribed to the difference in the ionic radius of Cu2+ and Zn2+ ions. The average crystallite size was determined using the Scherrer equation. The dc electrical resistivity of nanocrystalline starting composition Ni0.65Zn0.35Fe2O4 was few orders of magnitude higher than the bulk Ni0.65Zn0.35Fe2O4 prepared by conventional ceramic method. However, Curie’s temperatures and dielectric constant were decreased with increasing copper concentration. The observed variation in dc electrical resistivity and activation energy for conduction with Cu2+ substitution is attributed to changes in the microstructure, structural defects, and hopping mechanism.

Magnetic, structural and dc electrical resistivity studies on the divalent cobalt substituted Ni–Zn ferrite system

Polycrystalline cobalt substituted Ni – Zn ferrite with composition Ni 0.65-x Co x Zn 0.35 Fe 2 O 4(x = 0.00–0.25 insteps of 0.05) have been prepared through the conventional solid state ceramic method. Calcination and sintering have been performed in air atmosphere at 950°C and 1250°C for 4 h and 2 h, respectively followed by natural cooling to room temperature. X-ray diffraction patterns of all samples indicated the formation of the single spinel structure and the accurate lattice parameter for each composition has been determined using the Nelson–Riley error function. The increase in lattice constant on cobalt substitution is attributed to the ionic radius difference between the displaced and the substituted ion. The variation in lattice constant on incorporation of Co 2+ ion indicates its solubility into the spinel lattice and noticeable modification in structural properties have been observed. The observed increase in the saturation magnetization and Curie temperature with the increase in the Co 2+ substitution is due to its higher magnetic moment compared to that of Ni 2+, improvement in the A–B exchange interaction mechanism and large positive contribution to magnetic anisotropy due to presence of Co 2+ when they are at the octahedral sites. The observed variation in the initial magnetic permeability and the magnetic loss factor with cobalt substitution measured at a low frequency of 1 KHz have been attributed to the modification in the density, porosity, grain size and anisotropy contributions. A nearly comparable variation is observed in the room temperature dc electrical resistivity and activation energy for conduction and is attributed to the modification in structure, role and nature of cobalt ions and the microstructure aspects like grain size and pore concentration. The activation energy values in the range of 0.28 to 0.36 eV suggest a possible electron hopping. The observed changes in the structural and the magnetic and electrical properties have all been discussed in the light of exiting understanding.

Combustion synthesis of nano-crystalline Bi2/3Cu3Ti2.90Fe0.10O12 using inexpensive TiO2 raw material and its dielectric characterization

Nano-crystalline Bi2/3Cu3Ti2.90Fe0.10O12 powder was synthesized using a glycine–nitrate solution-combustion process, and applying inexpensive and stable solid TiO2 powder as the titanium source at relatively lower temperature than conventional ceramic methods. X-ray diffraction pattern confirmed the formation of a single phase of the ceramic sintered at 900°C for 12h. Bright-field transmission electron microscopy of the ceramic revealed that particle size is 16±07nm. Scanning electron microscopy image showed the presences of bimodal distribution of grains and the grain sizes were found to be in the range of, 500nm–1.5μm. Energy dispersive X-ray analyses confirmed the purity and stoichiometry of the ceramic. The frequency-dependent AC conductivity spectra obeyed the Jonscher's power law. The impedance spectroscopy study revealed the presence of grain boundary and electrode effects, which were also proved from modulus spectroscopy. The activation energies for grain boundaries and electrode effects were found to be 0.51 and 0.47eV, respectively.

Composition-related structural, thermal and mechanical properties of Ba1−xSrxTiO3 ceramics (0 ≤ x ≤ 0.4)

The Ba1−xSrxTiO3 (BST) ceramics were prepared by conventional ceramic method. The crystalline structure and morphology were studied by X-ray diffraction and scanning electron microscopy, respectively. Experimental results show that increase of sintering temperature leads to an uncontrolled precipitating of the phase with a lower content of Ti. The dielectric constant and specific heat as a function of composition and temperature were investigated. The increasing concentration of Sr ions leads to a shift of the Curie point below room temperature. To determine the elastic constants (the Young's modulus E, the shear modulus G and the Poisson's ratio v) of BST, a method of measurement of the longitudinal (νL) and transverse (νT) ultrasonic wave velocities for this type of material was developed. The structural, dielectric and mechanical properties of BST ceramics were discussed in terms of microstructure and chemical composition

(1 − x)(Bi,Na)TiO3−x (Ba,Sr)TiO3 lead-free piezoelectric ceramics for piezoelectric energy harvesting

Lead-free piezoelectric (1 − x)(Bi0.5Na0.5)TiO3−x (Ba0.5Sr0.5)TiO3 (x = 0, 0.03, 0.06, 0.08, 0.12) ceramics were fabricated by using a conventional ceramic sintering method. The piezoelectric properties of (1 − x)(Bi0.5Na0.5)TiO3−x (Ba0.5Sr0.5)TiO3 lead-free ceramics were investigated. The crystallinity and the microstructure of (1 − x)(Bi0.5Na0.5)TiO3−x (Ba0.5Sr0.5)TiO3 ceramics were observed employing X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The morphotropic phase boundary (MPB) of the rhombohedral and the tetragonal phases was detected at x = 0.08 by using the XRD patterns. In addition, the piezoelectric and the dielectric properties of (1 − x)(Bi0.5Na0.5)TiO3−x (Ba0.5Sr0.5)TiO3 were characterized. A piezoelectric coefficient d33 of 118 pC/N, an electromechanical coupling factor k p of 35.17%, a generated output power of 17.15 nW, and a figure of merit of 2.85 pm2/N were obtained.

Effects of sintering temperature on the piezoelectric properties of (Bi,Na)TiO3-based composites for energy harvesting applications

The effects of sintering temperature on the piezoelectric properties of (Bi,Na)TiO3–(Ba,Sr)TiO3 lead free ceramics were investigated. Lead free 0.97(Bi0.5Na0.5)TiO3–0.03(Ba0.5Sr0.5)TiO3 ceramics were fabricated by a conventional ceramic sintering method. The microstructure, crystal structure, and piezoelectric properties of the lead free 0.97(Bi0.5Na0.5)TiO3–0.03(Ba0.5Sr0.5)TiO3 piezoelectric ceramics were investigated by varying the sintering temperature from 1125 to 1225°C. The composites obtained at optimum conditions showed piezoelectric charge coefficient d33 of 108pC/N, electromechanical coupling factor kp of 33.9%, mechanical quality factor Qm of 227.9, relative dielectric permittivity εr of 613.1, the figure of merits of 2.14pm2/N and the generated output power of 25.48nW/cm2 were obtained. Our researches indicate that optimized sintering temperature and processing conditions can improve the piezoelectric properties of lead free 0.97(Bi0.5Na0.5)TiO3–0.03(Ba0.5Sr0.5)TiO3 ceramics.

Electrical, magnetic and magnetodielectric properties in ferrite-ferroelectric particulate composites

Particulate composites of ferroelectric and ferrite phases having general formula (1-x) {(Bi0.5Na0.5)0.94Ba0.06TiO3} − xNi0.65Zn0.35Fe2O4 were prepared for x = 0, 0.1, 0.2 and 0.3 using the conventional double-sintering ceramic method. The structural analysis were carried out to confirm the presence of constituent phases in the composite and to evaluate lattice parameter for all samples. The microstructural analysis and average grain size determination were carried out using a field emission scanning electron microscope (FESEM). The dielectric properties were measured as a function of temperature and frequencies. Observations of P-E hysteresis loops and M-H hysteresis loops, respectively, confirm the ferroelectric and ferromagnetic nature of the composite samples, and the coupling between ferroelectric and ferromagnetic ordering was ensured in the presence of a magnetodielectric at room temperature. The highest value of the magnetodielectric is found to be 2.19% for 30 mol% of NZFO. The investigated composites seem to be very attractive for multiple state memory devices in which data can be stored as polarization (P) or magnetization (M) or both.

Relation between the microstructure and the electromagnetic properties of BaTiO3/Ni0.5Zn0.5Fe2O4 ceramic composite

The microstructure–property relation in ferroelectric/ferromagnetic composite is investigated in detail, exemplified by typical sol–gel-derived 0.3BTO/0.7NZFO ceramic composite. The effect of microstructural factors including intergrain connectivity, grain size and interfaces on the dielectric and magnetic properties of the composite prepared by conventional ceramic method and three-step sintering method is discussed both experimentally and theoretically. It reveals that the dielectric behavior of the composite is controlled by a hybrid dielectric process that combines the contribution of Debye-like dipoles and Maxwell–Wagner (M–W or interfacial) polarization. Enhanced dielectric, magnetic and conductive behaviors appear in the composite with better intergrain connectivity and larger grain size derived by sol–gel route and three-step sintering method. The effective permittivity contributed by Debye-like dipoles exhibits a value of ~130,000 in three-step sintered composite, which is almost the same as that in conventionally sintered one, but that contributed by M–W response is much smaller in the former. Compared with conventionally prepared samples, the relaxation time (τ) is 3.476 × 10−6 s, about one order of magnitude smaller, and the dc electrical conductivity is 3.890 × 10−3 S/m, one order of magnitude higher in three-step sintered composite. The minimum dielectric loss reveals almost the same (~0.2) for all samples, but shows distinguishable difference in low-frequency region. Meanwhile, an initial permeability of 84, twice as large as that of conventionally prepared composite and 56 % the value of single-phased NZFO ferrite (~150), and a saturation magnetization of 63.5 emu/g, 32 % higher than that of conventional one and approximately 84 % the value of single-phased NZFO ferrite (~76 emu/g), appear simultaneously in three-step sintered composite with larger grain size and better intergrain connectivity. It is clear that the discovery is helpful for establishing a more explicit view on the physics of multi-functional composite materials, while the composite with optimized microstructure is beneficial to be used as a high-performance material.

Effects of SiO2 concentration on the DC-bias-superposition characteristics of the NiCuZn ferrites

DC-bias superposition characteristics of low-temperature-fired NiCuZn ferrites have been investigated for the stability of magnetic components. Different amount of SiO2 doped NiCuZn ferrites (low-permeability-composition, group A and high-permeability-composition, group B) were prepared by the conventional ceramic method. All XRD patterns of A and B exhibited single spinel phase, while the average grain size and sintered density gradually decreased with increasing SiO2 content, 0.35 wt% SiO2 doped ferrite A possessed similar permeability with 0.75 wt% SiO2 doped ferrite B. The latter sample presented a better DC-bias-superposition characteristic owing to the thicker nonmagnetic grain boundary and the higher coercivity. The declining rate of incremental permeability under high superposition magnetic fields was slower for the ferrite B with more SiO2 addition, indicating a better DC-bias superposition characteristic for electronic devices.