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Mono and co-substitution of Sr2+ and Ca2+ on the structural, electrical and optical properties of barium titanate ceramics
摘要： In this work, Ba0.9Sr0.1TiO3, Ba0.7Sr0.3TiO3, Ba0.5Sr0.5TiO3, Ba0.5Ca0.25Sr0.25TiO3 and Ba0.5Ca0.5TiO3 have been synthesized to evaluate the influence of mono and co-substitution of A-site dopants (Sr2+ and Ca2+) on the structural, electrical and optical properties of BaTiO3 ceramics. Sr2+ added samples showed a tetragonal structure which became slightly distorted with increasing Sr2+ concentration and finally achieved a cubic structure for x = 0.50. Ba0.5Ca0.5TiO3 also retained their tetragonality with limited solubility. Presence of second phase, CaTiO3 demonstrated the fact of restricted solubility. The concurrent effect of Sr2+ and Ca2+ didn't alter the tetragonal structure. Sr2+ substitution enhanced the apparent density as well as grain size which stimulated the domain wall motion and improved dielectric properties. However, the ferroelectric nature of Ba1-xSrxTiO3 was poor due to the redistribution of point defect at grain boundary. The optical band gap was found to be reduced from 3.48 eV to 3.28 eV with increasing Sr2+ content. Co-substitution of cations improved the electrical property significantly. The highest value of dielectric constant was found to be ～547 for Ba0.5Ca0.25Sr0.25TiO3 ceramics. Both Ba0.5Ca0.25Sr0.25TiO3 and Ba0.5Ca0.5TiO3 had developed P-E loop having lower coercive field and moderate optical band gap energy. Co-doping with Sr2+ and Ca2+ was a good approach enhancing materials electrical as well as optical property.
关键词： Dielectric properties,Grain size,X-ray diffraction,Optical properties,Sintering
更新于2025-11-21 11:18:25
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TiO2 Rutile phase formed interlayers by sintering mono phasic bioceramics for Biomedical applications
摘要： The formation of rutile TiO2 phase in nanoHydroxyapatite(nanoHAP) coated titanium metal (nanHAP- TiO2-Ti) is reported. This work is mainly emphasized in order to enhance the corrosion protection performance, osseointegration and biocompatibility. The optimized potential of nanoHAP coated titanium using electrophoretic deposition (EPD) was found to be 80 V and 3 minutes. The coated samples were sintered in air at various sintering temperatures from 600 to 900°C for 1 hour. The crystallinity, vibrational states, surface morphology and surface topography were characterized by XRD, Raman, FESEM with EDAX and AFM studies respectively. In the present work, investigations on the corrosion behavior of sintered sample in Ringer’s solution by means of electrochemical studies using Open Circuit Potential (OCP), Electrochemical Impedance spectroscopic(EIS) and anodic polarization studies were carried out. The electrochemical studies exhibited an enhanced corrosion resistant behaviour towards nanoHAP coated titanium sintered at 800oC with complete rutile TiO2 phase formation. The in vitro cytotoxicity studies of the coated materials were carried out by MTT assay and cell attachment with osteoblast cells. These studies revealed an enhanced cell attachment and proliferation on the composite layer compared to uncoated metal, which controlled the release of metal ions into the biological system.
关键词： Biocompatibility,nanHAP- TiO2-Ti,EPD,EIS,Sintering
更新于2025-11-21 11:08:12
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Spectral analysis and temperature measurement during flash sintering under AC electric field
摘要： In-situ diffraction experiments were used to study the change in peak profiles of 8YSZ during conventional sintering and flash sintering under AC electric field. Using calibration from a conventionally heated standard, the lattice expansion of 8YSZ under flash conditions was correlated to actual specimen temperature, indicating temperature comparable to that required for conventional sintering. At higher current densities, a temperature rise greater than 2000 °C was reached, which resulted in abnormal grain growth and temperature instability. Microstructural analysis demonstrated that finer grain size can be achieved by limiting the current in order to avoid high specimen temperatures. Experiments varying the thickness of the green compact resulted in higher heat loss due to thermal conduction and corresponding reduction in final density. A replacement to the blackbody radiation model was successfully used to fit the data and explain all effects based on Joule heating as well as provide a flash sintering processing map incorporating furnace temperature, power dissipation, and sample geometry.
关键词： 8YSZ,processing map,fast firing,flash sintering,energy dispersive diffraction
更新于2025-11-21 11:01:37
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Grain growth mechanism and thermoelectric properties of hot press and spark plasma sintered Na-doped PbTe
摘要： We investigated he thermoelectric (TE) properties and microstructures of Na-doped PbTe compounds, synthesized by various milling and sintering processes. It has been generally accepted that spark plasma sintering (SPS) inhibits grain growth due to the short sintering time, which is bene?cial to the nano bulk composite. In contrast, we observed abnormal grain growth for SPS, unlike hot press (HP) sintering. Considering the Gibbs free energy change during sintering, the HP sintering increases internal energy while the SPS increases entropy energy, which causes the abnormal grain growth. Lattice strain and Fourier transform analyses of the transmission electron microscope images showed that the SPS sintered samples had more signi?cant lattice strains and defects than the HP sintered samples. The low thermal conductivity of the SPS sintered samples was not from grain boundary phonon scattering but from phonon scattering by lattice strains and defects. The lattice strains and defects decreased electrical conductivity as well, resulting in deterioration of the power factor and thermoelectric performance. This suggests that the lattice strains and defects are more critical factors for enhancing thermoelectric per- formance than particle and grain size control.
关键词： Grain growth,Thermoelectric,Hot press,Spark plasma sintering,ZT
更新于2025-11-21 10:59:37
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Dielectric tunable properties of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics prepared by spark plasma sintering
摘要： Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics were prepared by spark plasma sintering (SPS) technique and their phase composition, microstructures and dielectric tunable properties were studied. With increasing Mg2TiO4?MgO content, the dielectric peaks of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics were broadened and suppressed. The tunability of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics first increased and then decreased with the increase of Mg2TiO4?MgO content. For Mg2TiO4?MgO content ≤ 50 wt%, Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics showed higher tunability and lower permittivity than pure Ba0.5Sr0.5TiO3, which can be attributed to the suppression of the doping effect by SPS. The contradiction between reduced permittivity and enhanced tunability in ferroelectric-dielectric composites was resolved.
关键词： Dielectrics,Ferroelectric ceramics,Spark plasma sintering,Composites
更新于2025-11-14 17:28:48
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Improved densification behavior and energy harvesting properties of low-temperature sintered (Ba, Ca)(Zr, Ti)O3 piezoceramics with a CuO additive
摘要： Piezoelectric energy harvesting has recently attracted substantial interest because of its ability to provide sustainable power for devices that consume very small amounts of energy. In this work, we propose a CuO-doping strategy to develop environmentally friendly (Ba, Ca)(Zr, Ti)O3 (BCZT) piezoelectric energy harvesters with both low sintering temperatures and excellent power generation performance. The CuO dopant greatly promoted the densification behavior of BCZT ceramics, yielding a densified and fine-grained microstructure at a sintering temperature reduced by 125°C compared to that of undoped BCZT. Moreover, CuO addition substantially reduced the domain size compared to that of the undoped BCZT and thus facilitated domain switching in the ceramics. While maintaining the Curie temperature (Tc) at ~120oC, 0.50 mol% CuO-doped ceramics exhibited significantly enhanced electromechanical properties with a figure of merit d33×g33 of 6661×10-15 m2/N, high-field piezoelectric constant d33* of 873 pm/V, electromechanical coupling factor kp of 0.53 and energy conversion efficiency η of 97%. A high power density of 1.8 μW/mm3, which corresponds to a ~360% improvement relative to that of the undoped BCZT, was achieved from 0.50 mol% CuO-doped BCZT energy harvesters at 10 m/s2 acceleration. These findings suggest the tremendous potential of CuO-doped (Ba, Ca)(Zr, Ti)O3 piezoceramics in high-power-density energy harvesting applications.
关键词： A. Sintering,C. Electrical properties,D. BaTiO3,B. Microstructure
更新于2025-11-14 17:28:48
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Particle transport mode during flash sintering of sodium bismuth titanate ceramic
摘要： In this work, the NBT ceramics are successfully flash sintered at a direct current 30 mA/mm2 for 30 s under different initial electric field. Subsequently, the actual temperature of samples is estimated by blackbody radiation theory under different conditions. The calculation results show that the sample temperature is close to the densification temperature of NBT ceramics used in conventional method. The rapid densification mechanism is discussed by wetting of local contact particles due to the asymmetrical Joule heating. In particular, we analyzed the particle transport mode during flash sintering in terms of particle diffusion. It is believed that the transform in the particles transport mode from solid diffusion to flow mass transfer accelerated the particles diffusion rate, which ensure the particle rearrangement and achieve the local shrinkage of particles in a short period of time.
关键词： Flow mass transfer,Flash sintering,Joule heating,Particles transport
更新于2025-11-14 14:48:53
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Simultaneous realization of broad temperature stability range and outstanding dielectric performance in (Ag+, Ta5+) co–doped TiO2 ceramics
摘要： Effects of sintering condition on dielectric properties and microstructure were systematically investigated in (Ag1/4Ta3/4)0.005Ti0.995O2 ceramics. A giant dielectric constant of ~9831 (1 kHz) and a relatively low dielectric loss of ~0.041 (1 kHz) were realized at the optimal sintering condition of 1330 °C with a holding time for 10 h. Notably, stable temperature coefficient (within -6.8% to 8.8%) of the dielectric constant at 10 kHz was achieved in a broader temperature range (-200–200 °C), which shows superior temperature stability of our sample than the application requirements (-55~200 °C and ?εr/ε25 °C < ±15%) of commercial X9R capacitor.
关键词： sintering conditions,dielectric properties,ceramics,temperature stability
更新于2025-09-23 15:23:52
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Temperature independent low firing [Ca0.25(Nd1-xBix)0.5]MoO4 (0.2 ≤ x ≤ 0.8) microwave dielectric ceramics
摘要： A scheelite structured [Ca0.25(Nd1-xBix)0.5]MoO4 (0.2 (cid:1) x (cid:1) 0.8) ceramics were prepared via solid state reaction method. All the ceramics can be well densi?ed below 780 (cid:3)C. As x value increased from 0.2 to 0.8, microwave dielectric permittivity increased from 14.0 to 27.8, Qf (Q ? quality factor ? 1/dielectric loss; f ? resonant frequency) value decreased from 42,000 GHz to 19,000 GHz, and TCF shifted from (cid:4)50 ppm/oC to t18 ppm/oC. The best microwave dielectric properties with permittivity between 23.54 and 23.56, Qf value between 24,000 GHze21,000 GHz and TCF value ~ (cid:4)8 ppm/oC in wide temperature range 25 (cid:3)Ce130 (cid:3)C were obtained in x ? 0.6 ceramic. This work showed that Bi played an important role to modify the TCF from negative to positive value in scheelite materials and this result further accelerate the application of scheelite materials in low temperature co-?red ceramics (LTCC) technology.
关键词： Microwave dielectric properties,Low temperature sintering,MoO3,Scheelite
更新于2025-09-23 15:23:52
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Bonding of Large Substrates by Silver Sintering and Characterization of the Interface Thermal Resistance
摘要： Low-temperature silver sintering technology, which has been proven to be a promising die-attach solution, was extended to bonding large substrates. Strong bonding strengths for substrates greater than 25 mm × 50 mm were achieved by sintering a nanosilver paste at temperatures below 270oC with less than 5 MPa pressure. To characterize the thermal performance of the substrate-attach interface, we applied a transient thermal technique with cumulative structure function analysis. Using self-heating and temperature-sensitive threshold voltage of a power device, we measured the transient thermal responses of the device placed at various locations on the bonded structures. Each transient thermal response was used to determine cumulative structure function, which represents the relationship between cumulative thermal capacitance and cumulative thermal resistance from the device junction to the ambient environment. Two-dimensional maps corresponding to interface thermal resistance were obtained from structure function plots. We found that for well-bonded substrates, the average specific thermal resistance contributed by the sintered silver interface was between 5.20 mm2K/W and 5.78 mm2K/W with a variation of 4.7% to 6.0%.
关键词： silver sintering,Substrate-attach,two-dimensional map of interface thermal resistance,transient thermal characterization
更新于2025-09-23 15:23:52