Conventional Sintered Samples Research Articles

Microstructure, dielectric and ferroelectric properties of (1−x) BaTiO3–xBiYbO3 ceramics fabricated by conventional and microwave sintering methods

(1−x) BaTiO3–xBiYbO3 (abbreviated as (1−x) BT−xBY, x = 0, 0.03, 0.06 and 0.09) ferroelectric ceramics have been fabricated by conventional sintering (CS) and microwave sintering (MWS) methods. The microstructure, dielectric and ferroelectric properties of (1−x) BT–xBY ceramics have been investigated systematically. X-ray diffraction patterns indicate all samples possess single perovskite phase and the crystal structure transforms from tetragonal to pseudo-cubic phase with increasing x. It can be also found that denser microstructure and finer grains can be obtained by MWS compared to CS as indicated by scanning electron microscopy. Dielectric measurements reveal that the addition of BY can lead to an obvious relaxation behavior in all samples, and the relaxation characteristics of MWS samples are stronger than those of CS samples. Moreover, the dielectric constant decreases with increasing BY content and the temperature stability and frequency stability of dielectric properties can be enhanced by using MWS method and addition of BY. P–E hysteresis loops become slimmer with the increase of BY content, and the ferroelectric properties of MWS samples are similar to those of CS samples. The leakage current of MWS sample is smaller than that of CS sample from J–E curve. The energy storage efficiency (η) increases with increasing BY content, while the energy storage density (U) increases and then decreases, Umax is obtained at x = 0.06. These results demonstrate that MWS technique and moderate BY content are effective methods to prepare materials for energy storage application.

Effects of sintering method and BiFeO3 dopant on the dielectric and ferroelectric properties of BaTiO3–BiYbO3 based solid solution ceramics

(0.95–x) BaTiO3–0.05 BiYbO3–x BiFeO3 (x = 0, 0.01, 0.02, and 0.04) (abbreviated as (0.95–x) BT–0.05 BY–x BFO) ceramics were fabricated by conventional sintering (CS) and microwave sintering (WS) methods. Effects of sintering method and BFO dopant on the microstructure and electric properties of (0.95–x) BT–0.05 BY–x BFO ceramics were comparatively investigated. X-ray diffraction showed that all CS and WS samples presented a single perovskite phase. It was also found that WS ceramics possessed denser microstructure and finer grains compared to CS samples as indicated by the surface morphology characterization. Dielectric measurements revealed that all samples exhibited the weak relaxation behavior; however, the degree of relaxation behavior of BT–BY based ceramic could be strengthened by addition of BFO and by WS method. Moreover, the temperature and frequency stability could be improved with doped BFO. The density of 0.93BT–0.05BY–0.02BFO ceramic was found to be the largest while that of 0.94BT–0.05BY–0.01BFO ceramic was the smallest, thus, the dielectric constant of 0.93BT–0.05BY–0.02BFO was significantly larger than that of 0.94BT–0.05BY–0.01BFO and 0.94BT–0.05BY–0.04 BFO ceramics. minimum dielectric constant of (0.95–x) BT–0.05 BY–x BFO ceramic was obtained at x = 0.01. Ferroelectric measurements indicated that all samples showed the slim hysteresis loop. The remnant polarization (Pr) and coercive field (EC) of (0.95–x) BT–0.05 BY–x BFO ceramics first decreased and then increased with increasing x，the minimum values were obtained at x = 0.01. Moreover, Pr and EC of WS ceramics were slightly larger than those of CS ceramics, indicating that higher density and larger grain sizes contributed to enhancing the ferroelectric characteristic. These findings indicate that addition of moderate amount of BFO and use of WS technique can strengthen the degree of relaxation behavior and improve the ferroelectric properties of BT–BY based ceramics.

A comparative study of lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.08Sn0.02)O3 ceramics prepared by conventional sintering and microwave sintering techniques

A comparative study on the lead-free ((Ba0.85Ca0.15) (Ti0.9Zr0.08Sn0.02)O3 (BCZTS)) piezoelectric ceramics prepared by conventional sintering (CS) and microwave sintering (MWS) techniques has been conducted. Samples fabricated by CS and MWS techniques showed pure ABO3 perovskite structure in XRD patterns. High-density ceramic materials were obtained in both CS and MWS ceramics. The microstructure of MWS samples is more homogeneous and less porous than CS samples. In addition, the grain size of MWS specimens is larger than the CS one at the same temperature. The piezoelectric property of both samples was measured, the result showed that both d33 and kp were higher for MWS samples compared to CS samples. The dielectric property of both samples was measured in the frequency range of 100Hz–1MHz. The typical relaxor behavior was observed in both types of samples confirmed by diffuse phase transition and frequency dispersion. Tc of MWS ceramics was lower than CS ceramics when 1220°C ≤ T ≤ 1340°C, while Tc of MWS ceramics was higher than CS ceramics when T = 1380°C. The ferroelectric property was tested at 3kV and 1Hz, the result exhibited that both CS and MWS ceramics were good ferroelectric materials.

Structural and magnetic properties of spark plasma sintered Co-Mg-Zn substituted Ba-Sr hexagonal ferrite magnets

The effect of conventional and spark plasma sintering processes on the structural and magnetic properties of Ba0.5Sr0.5Fe12−2xCox(MgZn)x/2O19 (x=0.2, 0.4 and 0.6) was investigated in this study. XRD patterns of both conventionally sintered (CS) and spark plasma sintered (SPS) samples with x=0.2 and 0.4 showed the crystallization of Ba0.5Sr0.5Fe12O19-phase with space group of P63/mmc. However, in the case of SPS sample with x=0.4, a secondary peak of α-Fe2O3 was observed. SEM analysis on the SPS samples revealed dense morphology with low porosity; while the CS samples showed the presence of aggregated particles with spherical shapes. Maximum values of saturation magnetization, MS (58emu/g) and coercivity, HC (3.5kOe) were obtained for the CS samples with x=0.4; while their SPS counterparts revealed increased MS (65emu/g) and HC (3.9kOe) values. The observed magnetization reversal behaviour for both sintering conditions were not smooth in the case of x=0.2, which indicated the existence of two-phase behavior. The temperature dependent magnetization studies for x=0.2 and 0.4 were performed in order to analyze the variation in Curie temperature against Co-Mg-Zn substitution and the obtained results are discussed on the basis of crystallization of hexaferrite-phase.

Comparison of structure and electrical properties of vacuum-sintered and conventional-sintered Ca1-xYxCeNbWO8 NTC ceramics

The effects of vacuum sintering and conventional sintering on the structure and high-temperature electrical properties of Ca1-xYxCeNbWO8 ceramics have been comparatively studied. X-ray diffraction (XRD) result shows that the conventional-sintered ceramic is a single CaWO4 phase with a scheelite structure, whereas the vacuum-sintered ceramics are composed of a major CaWO4 phase with scheelite structure and a minor CeNbO4 phase with fergusonite structure. The grain size of the conventional-sintered Y-doped ceramics is smaller than that of the undoped samples. The grain size of the vacuum-sintered samples increases firstly and then decreases with increasing the Y concentration. The activation energy of the conventional-sintered and vacuum-sintered ceramics all decreases with increasing the Y content. The activation energy of the vacuum-sintered samples is smaller than that of conventional-sintered samples at the given compositions. The change of activation energy should be attributed to the variation of Ce3+ ion concentration.

Induced anisotropic behavior and enhanced electrical properties on hot-pressed strontium barium niobate ceramics

Sr0.30Ba0.70Nb2O6 (SBN30) ferroelectric ceramics were fabricated by conventional sintering (CS) and by hot-pressing sintering (HP) and their crystal structure, microstructure, dielectric, ferroelectric and pyroelectric properties were studied and compared. Preferred orientation of the HP ceramics was detected through X-ray diffraction. Dense microstructure virtually free of pores has been achieved in HP samples. Moreover, the HP samples manifested prominent anisotropy in electrical properties. Besides, the relative permittivity (εr), saturated polarization (Ps), pyroelectric coefficient (p) in the direction perpendicular to the pressing axis were much higher than those of the randomly oriented CS samples. The HP samples sintered under 200MPa show excellent pyroelectric properties in the direction perpendicular to the pressing axis, with pyroelectric coefficient of 2.38×10−8C/cm2K and pyroelectric figure of merit of Fi=1.13pm/V, Fv=1.89m2/C and Fd=0.63 μPa−1/2，which roughly triple the values obtained in CS samples. These results indicate that hot-pressing is a viable option for accessing single-crystal-like anisotropy as well as enhanced electrical properties in polycrystalline ceramics, thus unveiling the distinctive potential of HP SBN30 ceramics for infrared detector applications.

Microwave sintering of ceria-doped scandia stabilized zirconia as electrolyte for solid oxide fuel cell

In this work, the effect of microwave sintering on the properties of 1 mol% ceria-doped scandia stabilized zirconia (10Sc1CeSZ) was investigated. The sintering was carried out at temperatures 1300 °C and 1350 °C for 15 min using a 2.45 GHz microwave furnace. The sintering behavior of the microwave sintered ceramics was compared with that obtained via the conventional sintering at temperatures ranging from 1300 °C to 1550 °C with 2 h holding time. It was found that both sintering processes yielded highly dense samples with minimum density of 98% theoretical value. Phase analysis by X-ray diffraction revealed the presences of only cubic phase in all sintered samples. All sintered pellets possessed high Vickers hardness (13–14.6 GPa) and fracture toughness (∼3 MPa m1/2). Microstructural examination by using the scanning electron microscope showed that the grain size varied from 2.9 to 9.8 μm for the conventional sintered samples whereas the grain size of the microwave sintered ceramics was below 2 μm. Electrochemical Impedance Spectroscopy study recorded the maximum ionic conductivity of 0.280 S/cm at 800 °C for the conventional-sintered sample at 1550 °C whereas a high value of 0.314 S/cm was measured for the microwave-sintered sample at 1350 °C.

Effects of sintering on the mechanical and ionic properties of ceria-doped scandia stabilized zirconia ceramic

The effect of conventional sintering from 1300 to 1550°C on the properties of 1mol% ceria-doped scandia stabilized zirconia was investigated. In addition, the influence of rapid sintering via microwave technique at low temperature regimes of 1300°C and 1350°C for 15min on the properties of this zirconia was evaluated. It was found that both sintering methods yielded highly dense samples with minimum relative density of 97.5%. Phase analysis by X-ray diffraction revealed the presences of only cubic phase in all sintered samples. All sintered pellets possessed high Vickers hardness (13–14.6GPa) and fracture toughness (~3MPam1/2). Microstructural examination by using the scanning electron microscope revealed that the grain size varied from 2.9 to 9.8µm for the conventional-sintered samples. In comparison, the grain size of the microwave-sintered zirconia was maintained below 2µm. Electrochemical Impedance Spectroscopy study showed that both the bulk and grain boundary resistivity of the zirconia decreases with increasing test temperature regardless of sintering methods. However, the grain boundary resistivity of the microwave-sintered samples was higher than the conventional-sintered ceramic at 600°C and reduced significantly at 800°C thus resulting in the enhancement of electrical conduction.

Effect of increasing lanthanum substitution and the sintering procedures on the properties of SrBi4Ti4O15 ceramics

Lanthanum-substituted SrBi4Ti4O15 (SBTi) ceramic, that is SrBi4−x La x Ti4O15 (SBLTi), samples were calcined by solid-state reaction and densified using the microwave sintering and conventional sintering techniques. Their structural, morphological and mechanical properties were investigated. The microwave sintered samples showed high densities like 95% of the theoretical density with short duration exposures. Compared with SBTi ceramics and other lanthanide-substituted compositions, the incorporation of La 3+ results in clear improvement in properties for SBLT (x ∼0.75) with respect to the values of hardness and Young’s modulus of the microwave sintered samples (8.8–12.5 and 160–180 GPa) are higher than that for conventional sintered (8–10 and 135–155 GPa) samples.

Preparation of m-ZrO2 compacts by microwave sintering

Dense un-doped monoclinic ZrO2 (m-ZrO2) compacts were prepared successfully by microwave sintering with a TE666 resonant mode and temperature ranges from 1350°C to 1550°C. XRD and SEM techniques were used to characterize the samples. A dense and homogeneous microstructure was observed with the grain size of 1μm, which is smaller than that of conventional sintered ones. A monoclinic ZrO2 phase without detectable tetragonal ZrO2 (t-ZrO2) was found for both microwave sintered and conventional sintered samples. Density of samples was measured according to the Archimedes principle. The results showed a relative density of 99.0% for microwave sintered samples which is higher than that of conventional sintered ones. The microhardness was investigated by indentation test with the highest value of 4.0GPa. Meanwhile, microcracks were observed on the edges of the indentation but not at the tips for microwave sintered samples which indicated good toughness. Optimized microwave sintering temperature of m-ZrO2 compacts was 1450°C for 30min with the microhardness of 4.0GPa and relative density of 99.0%.

A Comparative Research on PLMNT Relaxor Ferroelectric Ceramic Prepared by Conventional and Hot-Press Techniques

PLMNT3/75/25 ceramics were prepared by uniaxial hot-press sintering method and conventional sintering method, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer were used to measure the properties of the PLMNT ceramics. PLMNT ceramic with pure perovskite phase was fabricated by uniaxial hot-press sintering method, while, a secondary pyrochlore phase was found in PLMNT ceramic prepared by conventional sintering method. It was observed that the PLMNT ceramic fabricated by uniaxial hot-press sintering showed better densification and more uniform grain size than that of the PLMNT ceramic prepared by conventional sintering. The dielectric responses showed that the samples prepared by two methods both exhibited diffuse phase transition characteristic, and the values of the diffusivity parameter were calculated according to the linear fitting of the modified Curie-Weiss law. The relaxor ferroelectric characteristics of PLMNT ceramics accorded well with the Vogel-Fulcher relationship. The P-E hysteresis loops of the samples from uniaxial hot-press sintering were apparently slight than that of conventional sintering samples, while the value of the Ps (saturation polarization) was significantly higher.

A comparative study on positive temperature coefficient effect of BaTiO3–K0.5Bi0.5TiO3 ceramics by conventional and microwave sintering

Abstract As a promising material for lead-free positive temperature coefficient of resistivity (PTCR) ceramics, (1− x )BaTiO 3 – x K 0.5 Bi 0.5 TiO 3 ( x =0.002–0.008) samples were prepared by conventional sintering (CS) and microwave sintering (MS) techniques. The effects of different sintering method on the phase composition, microstructure and PTCR characteristics of the ceramics were investigated. The sintering cycle of ceramics was 2.5 h by MS, whereas it took 14 h by CS. Using the microwave heating, the sintering temperature to get high dense material is lowered by 40 °C compared to CS samples. The XRD results showed that all samples were pure tetragonal phases by both sintering process. Meanwhile, the MS samples had smaller grain size and uniform grain distribution. For PTC ceramics, MS was superior to CS due to rapid processing and uniform temperature distribution throughout the specimen. Thus, it exhibited improved PTC properties with lower room temperature resistivity ( ρ RT ), higher Curie temperature ( T c ) and steep resistance jump (lg( ρ max / ρ min )).

A comparative study of Sr0.7Ba0.3Nb2O6 relaxor ferroelectric ceramics prepared by conventional and microwave sintering techniques

Abstract Sr 0.7 Ba 0.3 Nb 2 O 6 (SBN70) ceramics were prepared by conventional sintering (CS) and microwave sintering (MWS) techniques. High-density ceramics were obtained by the MWS method in 2 h of cycle time, whereas it took 14 h by the CS method. Samples prepared by both sintering techniques showed single phase formation according to XRD results. It was observed that MWS SBN70 ceramics showed better densification and more uniform grain size than those of CS samples. The dielectric characteristics of both samples showed diffuse phase transition phenomenon features, which was confirmed by linear fitting of the modified Curie–Weiss law. Besides, the relaxor ferroelectric properties of both samples followed the Vogel–Fulcher relationship well. The value of spontaneous polarization ( P s ) and the P–E hysteresis loop for MWS samples were significantly higher and slimmer than those of the CS samples, respectively.

Dielectric properties of Ba1−xSrxTiO3 ceramics prepared by microwave sintering

A comparative study on the dielectric properties of Ba1−xSrxTiO3 (x=0.1–0.6) ceramics prepared by microwave sintering (MS) and conventional sintering (CS) has been done. It was found that MS samples need lower temperature and much shorter time than CS samples to obtain the same degree of densification. Compared with CS samples, MS samples possessed smaller grain size, better densification and more uniform grain growth. The dielectric properties of the samples were measured as a function of temperature. It was observed that the dielectric constant was higher for MS samples compared with that of CS samples especially in the ferroelectric phase.

Effect of microwave sintering on the structural and densification behavior of sol–gel derived zirconia toughened alumina (ZTA) nanocomposites

Zirconia toughened alumina (ZTA) nanocomposites with different zirconia contents (5–20mol%) were prepared by the sol–gel method. The prepared composites were sintered at 1300°C by both conventional and microwave techniques. The crystallinity, average grain size, microstructure and densification of the samples prepared by conventional and microwave sintering methods were compared. X-ray diffraction analysis shows that the microwave sintered samples possess higher tetragonality and also exhibit reduced particle size compared to conventional sintering. HR-SEM surface micrograph reveals that the microwave sintered samples have homogeneous particle size distribution with less degree of porosity. TEM analysis confirms uniform distribution of particles with an average particle size of 20nm for the microwave sintered sample. SAED pattern reveals that the microwave sintered samples possess improved crystallinity compared to conventional sintered samples. The apparent porosity and density of ZTA nanocomposites measured for different zirconia contents show that the densification of 97% could be achieved for the microwave sintered samples with higher content of zirconium.

Electrical behavior of Gd-doped CeO2 electrolyte ceramics sintered from nanopowders prepared by mechanical alloying process

The densification behavior of nanocrystalline Gd-doped ceria electrolyte, synthesized via mechanical alloying process, was investigated by means of the conventional pressure less sintering and the two-step sintering methods. The effect of the heating rate and the amounts of dopant on the sinterability of Ce1−x Gd x O(2−δ) x = 0.2 (2GDC) and x = 0.3 (3GDC) oxides was studied, which indicated that the gadolinium retards densification and grain growth in the final state of the conventional sintering and 2GDC samples reach 94% density at 1,550 °C. Subsequent investigation on the grain growth in the fully densified ceramics showed that lowering of the heating rate and increasing of the soaking time reduce the effect of dopant and cause samples to be densified to the higher theoretical density (97%) at lower temperatures (1,400 °C). Fully dense Gd-doped ceria ceramics with finest grain size (900–1,100 nm) can be obtained by two-step sintering method. Electrical conductivity measurement in the GDC samples was studied by impedance spectroscopy. The grain boundary conductivity in these specimens obtained by two-step sintering method was compared with normal sintered specimens. It is concluded that the reduced conductivity observed in the two-step sintering specimen is attributable to the microstructure changes obtained by increased of grain boundary resistivity.

Mechanical parameters of strontium doped hydroxyapatite sintered using microwave and conventional methods

The effects of ion substitution in hydroxyapatite (HA) on crystal structure and lattice stability is investigated in the green state and post sintering. The effects of ion incorporation on the biaxial flexural strength and hardness are also investigated. Sintering is carried out at 1200 °C using comparative conventional and microwave regimes. Post sintering, the effects of ion incorporation manifest as an increase in the lattice d-spacings and a reduction of the crystallite size. Some HA decomposition occurs with β-TCP stabilisation in conventional sintering (CS), but this phase is destabilised during microwave sintering (MS), generating α-TCP. Conventional sintering (CS) allows higher densification in the undoped samples. Overall, for the Sr-doped compositions, the MS samples retain higher amounts of HA and experience higher density levels compared to the CS samples.

Effect of Particle Size and Sintering Procedure on Microstructure, Dielectric, Ferroelectric and Mechanical Properties of SrBi4Ti4O15

Bismuth layered-perovskite compounds such as SrBi4Ti4O15 (SBTi) ceramics are prepared by solid state reaction. The SBTi ceramics are sintered by microwave and conventional sintering techniques. In this study, the effect of ball milling on different sintering processes, microstructure as well as on dielectric, ferroelectric and mechanical properties of SBTi ceramics is emphasized. The powder has been milled to produce nanocrystalline powders using a planetary ball mill. Different samples have been prepared by varying the milling time from 5 to 20 h, keeping the milling speed fixed at 300 rpm. The X-ray diffraction results show that crystalline powders with a single perovskite structure can be obtained when calcined at 700°C for 4 h. It has been observed that the average grain size, dielectric and ferroelectric properties are dependent on the duration of ball milling. The dielectric constant and loss tangent of the conventional sintered samples range between (140 and 165), and (0.05 and 0.07) respectively and those of the microwave sintered samples range between (155 and 175), and (0.04 and 0.06) respectively when measured at 1 MHz frequency. The microwave sintering process has been found to improve the homogeneity of the grains and morphology. The microwave sintering of the SBTi ceramics leads to higher densification (98% of the theoretical density), fine microstructure and good mechanical and ferroelectric properties in much shorter duration of time than that of conventional sintering process.

Microwave sintering of high-permeability MgCuZn ferrite at low sintering temperatures suitable for microinductor applications

Mg0.40Cu0.10Zn0.50Fe1.95O4-δ ferrite samples were prepared by the microwave sintering (MS) and conventional sintering (CS) techniques. The samples were then characterized by the x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS) techniques. All the compositions showed single-phase cubic spinel structure. The lattice constants of MS samples were found to have lower magnitude than those of CS samples. The densities of microwave-sintered samples were higher than those of conventionally sintered samples. The temperature dependence of initial permeability was studied in the temperature range 30–150 °C at 10° temperature intervals. It was noted that the initial permeability of MgCuZn ferrites prepared by the MS method was higher than that of MgCuZn ferrites prepared by the CS method. The initial permeability (μi) magnitude of about 2300 at 10 kHz is achieved for microwave-sintered (Mg0.40Cu0.10Zn0.50Fe1.95O4−δ) ferrite, at only 950 °C sintering temperature. In addition, the sintering time of ferrites was reduced from 5 h to 20 min by using the MS technique. The low-temperature-sintered MgCuZn ferrites prepared possess good electromagnetic properties, as well as good microstructure, thus making them suitable materials for multilayer chip inductors (MLCIs) having high performance and low cost.

Synthesis and Thermoelectric Properties of Ca<sub>2</sub>Co<sub>2</sub>O<sub>5</sub> Ceramics

The precursor of Ca2Co2O5 was prepared by coprecipitation method. The bulk Ca2Co2O5 samples were prepared by conventional sintering and Spark Plasma Sintering (SPS), respectively. The relative density of bulk Ca2Co2O5 ceramic, which was prepared by conventional sintering is about 75%; while the samples prepared by SPS has a density of 98%. The thermoelectric properties were enhanced by SPS, compared with samples prepared with conventional sintering. The maximum powerfactor of the conventional sintering and SPS samples are 2.70×10-4W∙m-1∙K-2 and 3.85×10-4 W∙m-1∙K-2, respectively.