CuO Sintering Research Articles

Effects of Bi2O3–CuO addition on the dielectric properties of MgO–TiO2(w) ceramics sintered at low temperatures

Herein, MgO–12 % TiO2(w) ceramics with different contents of Bi2O3–CuO sintering aid were prepared using a solid-state method. The effects of the sintering aid content on the sintering temperature and the dielectric and mechanical properties of the ceramics were studied. The material was characterized using scanning electron microscopy and X-ray diffraction and Precision LCR tester and universal testing machine and Archimedes drainage method. When the Bi2O3–CuO content was less than 9 wt%, the ceramic sample has higher dielectric properties. When the Bi2O3–CuO content was greater than 9 wt%, the dielectric properties will deteriorate. This is because Bi2O3 participates in the chemical reaction between MgO and TiO2, forming a high dielectric loss Bi4Ti3O7 phase. At high temperatures, Cu2+ can easily change valence to Cu+, promoting oxygen vacancies and increasing dielectric loss in ceramic samples. The introduction of Bi2O3–CuO produces new MgTiO3, Mg2TiO4, and Bi4Ti3O12 phases in the sample structure, resulting in a structure in which the MgO grains in the sample are surrounded by the new phases that appear around them. This structure fills the pores, increases density, enhances mechanical properties. The dielectric properties of the ceramics were the when the sintering temperature was 1050 °C, and the Bi2O3–CuO content was 3 wt%. The dielectric constant and dielectric loss were 11.19 and 1.17 × 10−4, respectively. The bending strength of the ceramic sample increased from 138.72 MPa to 179.64 MPa when the Bi2O3–CuO content was increased from 3 wt% to 15 wt%. The Bi2O3–CuO sintering aid enables MgO to be better applied in ceramic substrates.

Textured Pb(Mg1/3Nb2/3)O3 −Pb(In1/2Nb1/2)O3 −PbTiO3 ceramics with enhanced piezoelectric properties and high Curie temperature prepared by low-temperature sintering

A low-temperature sintering is crucial for the fabrication of multilayer piezoceramic actuators through low-cost internal metal electrodes. Herein, Pb(Mg1/3Nb2/3)O3−Pb(In1/2Nb1/2)O3 −PbTiO3 (PMN−PIN−PT) textured ceramics were prepared by a combined use of refined matrix powder and CuO sintering additive. When the matrix powder was refined by planetary ball-milling for 10 h, the sintering temperature of the textured 0.37PMN−0.29PIN−0.34PT ceramics was lowered to 1175 ºC, and a subsequent addition of 1 mol% CuO further lowered it to 950 ºC. The textured 0.37PMN−0.29PIN−0.34PT ceramics with 3 vol% BaTiO3 (BT) template sintered at 950 ºC for 10 h yielded excellent piezoelectric properties, such as a Lotgering factor (LF) of 97%, a unipolar strain of 0.23% at 2 kV/mm, and a Curie temperature (TC) of 231 ºC. These enhanced piezoelectric properties and high TC result from the high texture, transient liquid phase sintering, Cu2+ ion doping, and minimum BT template content.

Effects of sintering additives on defect chemistry and hydration of BaZr0.4Ce0.4(Y,Yb)0.2O3−δ proton conducting electrolytes

The effects of NiO, ZnO, and CuO sintering additives (0.5, 1.0, or 2.0 wt%) on the sintering behaviour, effective acceptor concentration, and hydration thermodynamics are examined for BaZr0.4Ce0.4Y0.1Yb0.1O3−δ and BaZr0.4Ce0.4Y0.2O3−δ proton conducting electrolytes. Thermogravimetry of hydration shows that the sintering additives – except for 0.5 wt% CuO – lead to a decrease in the effective acceptor concentration, and the decrease per mole sintering additive is the largest for NiO. The absence of typical secondary phases such as BaY2NiO5 and the homogeneous distribution of Ni determined from elemental mapping imply that sintering additives dissolve into the perovskite lattice. Exsolution of metallic Ni and Cu upon reduction leads to a substantial recovery of the effective acceptor concentration. Subsequent oxidation is accompanied by a repeated decrease in the effective acceptor concentration as the sintering additives appear to re-dissolve. Defect chemical reactions are proposed to explain the observed results and these are supported by energetics from first principles calculations. Overall, NiO has the highest positive impact on densification and grain growth, and a relatively small amount of 0.5 wt% NiO or CuO is preferable to optimise both sintering and hydration.

Competition of Li+ and Cu2+ ions dopant in BiAlO3–Pb(Zr,Ti)O3 piezoelectric ceramics in low temperature sintering processes

Sintering with sintering aids is widely used to achieve a low sintering temperature of lead-based piezoelectric ceramics. In this study, two low-temperature sintering aids, namely Li2CO3 and CuO, were doped into the x BiAlO3-(1-x) PZT + 0.2 wt% MnO2 composition, and the microstructures and electrical properties were investigated for these ceramics prepared via solid-phase reaction method. Differential Scanning Calorimetry (DSC) indicated that the Li2CO3 liquid phase formed at a lower temperature than that of CuO, while co-dopant of Li2CO3 and CuO will result in a competition between Li+ and Cu2+ ions during the low-temperature sintering processes, which negatively impacts piezoelectric properties. The results demonstrated that the piezoelectric properties of ceramics with only Li2CO3 or CuO additives are much better than ceramics with co-doped Li2CO3 and CuO additives. Ceramics with 0.3 wt% Li2CO3 or 0.1 wt% CuO sintering aid were sintered at 1000 °C, resulting in excellent piezoelectric coefficients (d33) exceeding 300 pC/N and mechanical quality factors (Qm) of 500 were obtained, respectively. This work provides inspiration for low-temperature sintering strategies in other ceramic materials.

The influence of sintering temperature on the microstructures and intermediate-temperature electrochemical properties of Ce0.8Sm0.1Yb0.1O2-α-CuO

In this study, Ce0.8Sm0.1Yb0.1O2-α (CSYb) was synthesized using a nitrate combustion method. CSYb added 2 wt% CuO sintering aid was also prepared at different sintering temperatures. The XRD, SEM and AC impedance spectroscopy were used to study the influence of sintering temperature on the structure and electrical performance of the samples. The XRD spectra indicated that the samples all had a good single-phase cubic fluorite structure. The SEM images showed that the grain sizes of the samples increased with the increase of sintering temperature. The conductivities of 1400-CSYb-CuO and 1450-CSYb-CuO reached 2.3 × 10−2 S.cm−1 and 2.8 × 10−2 S.cm−1 at 750 °C, respectively.

Process Development of Zirconolite Ceramics for Pu Disposition: Use of a CuO Sintering Aid

Zirconolite-structured ceramics are candidate wasteform materials for the immobilisation of separated Pu. Due to the refractory properties of zirconolite and other titanates, removing residual porosity remains challenging in the final wasteform product when utilising a conventional solid state sintering route. Herein, we demonstrate that the addition of CuO as a sintering aid increases densification and promotes grain growth. Moreover, zirconolite phase formation was enhanced at lower process temperatures than typically required (≥1350 °C). CuO addition allowed an equivalent density to be reached using process temperatures of 250 °C lower than the undoped composition. At 150 °C lower than the undoped zirconolite, the addition of CuO resulted in a favourable microstructure and phase assemblage, as confirmed via X-ray diffraction and scanning electron microscopy. Secondary phases of CaTiO3 and Ca0.25Cu0.75TiO3 were observed at some processing temperatures, which may prove deleterious to wasteform performance. The use of a CuO sintering aid provides an avenue for the further development of the thermal processing of ceramic wasteform materials.

The effect of sintering aids on BaCe0·7Zr0·1Y0.1Yb0.1O3-δ as the electrolyte of proton-conducting solid oxide electrolysis cells

Proton-conducting solid oxide electrolysis cells (H-SOECs) are attracting attentions of researchers due to their unique advantages. The proton-conducting material BaCe0·7Zr0·1Y0.1Yb0.1O3-δ (BZCYYb) has both the advantages of barium ceria-based and barium zirconate-based materials. BZCYYb material usually is synthesized by solid-state reaction (SSR) method, hence the densification of this electrolyte material is the key to restrict the application of H-SOECs. In this paper, effects of adding 1 wt% of different sintering aids (NiO, CuO, ZnO) to BZCYYb on the grain size and the conductivity are investigated. After adding 1 wt% of NiO and CuO sintering aids, BZCYYb electrolyte achieves ideal density. The electrical conductivity of four samples (BZCYYb without adding sintering aid, BZCYYb with 1 wt% NiO, CuO, ZnO, respectively) is tested under different steam concentrations of air, nitrogen, hydrogen, and nitrogen-hydrogen mixture. The conductivity increased after the sintering aid is added. With the increase of steam concentration, the conductivity decreased slightly and then increased due to electron holes under oxygen atmosphere with steam at high temperature. In other atmospheres, the conductivity increases with the steam concentration. In the atmosphere of 20 vol% H2O-Air and H2, the conductivity of the BZCYYb samples with 1 wt% CuO is about 1.087 × 10−2 S cm−1 and 9.02 × 10−3 S cm−1 at 650 °C, and the conductivity of the BZCYYb samples with 1 wt% NiO is 1.277 × 10−2 S cm−1 and 8.24 × 10−3 S cm−1, respectively. However, compared with NiO, CuO has advantages in promoting hydration reaction and proton conduction of BZCYYb electrolyte.

Influence of sintering activators on electrical property of BaZr0.85Y0.15O3-δ proton-conducting electrolyte

In this study, the influence of CuO and ZnO sintering activators on the densification behavior, distribution of sintering activators, and electrical properties of Y-doped BaZrO 3−δ proton conducting oxide were examined over a wide range of oxygen and water vapor partial pressures. With the use of 1 mol% CuO and 4 mol% ZnO, a relative density above 97% was achieved at sintering temperatures of 1500 °C and 1300 °C, respectively. The bulk and grain boundary conductivities of fully sintered BaZr 0.85 Y 0.15 O 3−δ , Ba(Zr 0.84 Y 0.15 Cu 0.01 )O 3−δ , and Ba(Zr 0.81 Y 0.15 Zn 0.04 )O 3−δ were assessed using electrochemical impedance spectroscopy. The amount of sintering activators incorporated into the bulk was investigated using an energy dispersive spectrometer equipped with a high-resolution transmission electron microscope, whereas the equilibrium concentrations of proton and oxygen vacancies as a function of water vapor pressure were estimated by thermogravimetric analysis. Using these results, the total electrical conductivities of the three compositions at 800 °C over a wide range of oxygen and water vapor partial pressures were analyzed via a non-linear fitting based on the defect structure of Y-doped BaZrO 3−δ . As a result, the proton, oxygen ion, and hole partial conductivities were calculated, and the proton transference numbers of the three compositions were compared. • Additions of CuO and ZnO in BZY effectively lower a sintering temperature • Cu was evenly distributed, whereas most of Zn was presented at grain boundaries • Concentration and mobility of proton in BZY-Cu and BZY-Zn were lower than BZY • Transference number of proton is in the order of BZY-Zn > BZY-Cu ≈ BZY

Effects of CuO Sintering Aids on Microstructure and Electric Properties for (Na0.48K0.473Li0.04Sr0.007) (Nb0.883Ta0.05Sb0.06Ti0.007)O3 Ceramics

In this paper, the effects of CuO sintering aids on microstructure and electric properties are investigated for the non-stoichiometric (Na0.48K0.473Li0.04Sr0.007)(Nb0.883Ta0.05Sb0.06Ti0.007)O3+x mol% CuO lead free ceramics. As the amounts of CuO equal 1 mol%, the sintering temperature is 975 °C and the piezoelectric parameters are d33 = 200 pC/N, g33 = 38 (10−3 Vm/N), d33 × g33 = 7600 (10−15 m2/N), kp = 0.38, Qm = 240, Pr = 18.93 μC/cm2 and EC = 8.75 kV/cm. The piezoelectric properties are changed to hard type and suitable for energy harvester with multilayer technology. The physical response mechanisms are suggested that the diffused phase transitions are enhanced, the Cu2+ ions substitute for the B-site ions with forming the Oxygen vacancies and the domain walls are pinning.

The electrical properties of low-temperature sintered 0.07Pb(Sb1/2Nb1/2)O3-0.93Pb(ZrxTi1−x)O3 multilayer piezoceramic actuator

0.07Pb(Sb1/2Nb1/2)O3-0.93Pb(ZrxTi1−x)O3 (PSbN-PZT) piezoceramics were fabricated at a low firing temperature of 920 °C using the LiBiO2, CuO and ZnO (LBCZ) sintering aids. The material samples exhibited excellent properties, including a converse piezoelectric coefficient d33* of ~558 pm/V, a relative dielectric permittivity εT33/ε0 of ~1725, a planar coupling factor kp of ~0.6 and a high Curie temperature Tc of ~308 °C, thus demonstrating the material suitability for use as a low-cost multilayer actuator. PSbN-PZT piezoceramic multilayer actuators with Ag/Pd internal electrodes were fabricated by tape casting method cofired at 920 °C. A large displacement of 1.45 μm was achieved in a single PSbN-PZT multilayer actuator (thickness = 2.0 mm) at the driving voltage of 125 V, while the displacement decreased ~27% under the mechanical stress of ~32 MPa. Good temperature stability was also exhibited in PSbN-PZT multilayer actuator, which was better than that of commercial PZT-5H ceramic. These results indicated that low-temperature fired PSbN-PZT multilayer actuator is a promising candidate device for commercial piezoactuator applications.

Maintaining pronounced proton transportation of solid oxides prepared with a sintering additive

This work reports key findings allowing a dense proton-conducting ceramic to be produced with a CuO sintering additive. A selection of this additive in low amounts results in materials exhibiting full proton capability and high ionic conductivity.

Solid-state reactive sintering of dense and highly conductive Ta-doped Li7La3Z2O12 using CuO as a sintering aid

Cubic-phase garnet-type Li7La3Z2O12 is a promising candidate for an electrolyte of all-solid-state lithium-ion batteries; however, its poor sinterability due to Li sublimation during firing has impeded large scale development. This study demonstrates a solid-state reactive sintering (SSRS) process with added CuO as a sintering aid to enable enhanced materials processing at lower temperatures. Applying the SSRS process with the addition of 1 wt% CuO decreased the sintering temperature for 0.5 mol%Ta-doped LLZTO pellets having over 90% relative density from 1250 to 1100 °C to reduce Li loss. The 1 wt% CuO addition did not lead to secondary phase formation as detected by XRD, nor to appreciable electronic conduction below 100 °C as measured by four-point probe method. The 1 wt% CuO-mixed LLZTO pellet exhibited high conductivity of approximately 3.0 × 10−4 S·cm−1 (bulk) and 5.45x10−5 S·cm−1 (grain boundary). The mechanism of CuO function as a sintering aid is presumed to be enabling liquid-phase sintering along with enhancing the decomposition of LiOH. The combined SSRS process along with optimized CuO sintering aid addition is a one-step process that is a practical technique to enhance the preparation of LLZO-based electrolyte for all-solid-state lithium-ion batteries.

High energy storage density realized in Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics at ultralow sintering temperature

The miniaturization and integration trend of electronic applications requires high energy storage performance, and the development of multilayer ceramic capacitors (MLCC) demands the compatibility between ceramic sintering temperature and co-firing temperature of metal electrodes. Herein, we obtained a high recoverable energy storage density and a low sintering temperature simultaneously in 0.5(Bi0.5Na0.5)TiO3-0.5SrTiO3-x mol% CuO (0.5BNT-0.5ST-x mol% CuO) via the combination of adding CuO sintering aid and citrate sol-gel synthesis method. The optimum sintering temperature decreases significantly from 1130 °C for x = 0 to 820 °C for x = 2.0. The ceramic of 0.5BNT-0.5ST-1.5 mol% CuO exhibits a large Wrec of 2.20 J/cm3 and η of 72.39% under 230 kV/cm. Furthermore, the same sample also possesses a large CD of 1740.97 A/cm2, an extremely high PD of 139.28 MW/cm3 and an ultrafast discharge speed of 82 ns. These merits reveal that the ceramic of 0.5BNT-0.5ST-1.5 mol% CuO has great potential in practical MLCC production.

Fast rate oxidation to Cu2O, at room temperature, of metallic copper films produced by the argon-plasma bombardment of CuO films

Using a powerful argon plasma equipment, 400 °C sintered CuO thin films were rapidly reduced to metallic copper for treatment times less than 35 s. The transformation caused the crystallographic plane of Cu to appear at the expense of the CuO ones. Likewise, transmittance spectra showed a rapid decline while reflectance spectra exhibited a fast increase towards the infrared region. The last effect was caused by the production of free electrons of metallic copper, which was also evidenced by a low electrical resistivity of 30 μΩ∙cm. The plasma-produced Cu samples displayed a fast oxidation rate at room temperature and atmospheric conditions, which has been rarely mentioned in literature. Interestingly, instead of CuO, the oxidation produced Cu2O films, which is a p-type semiconductor oxide with high potential for several applications. Even though it only requires some hours, the oxidation was allowed to take place for one week. X-ray diffraction, X-ray photoelectron spectroscopy, transmittance-reflectance, and resistivity measurements demonstrated the oxidation of Cu to Cu2O. Similar phenomena were confirmed for lower sintering temperatures of the CuO films. Nevertheless, the oxidation tendency of plasma-obtained Cu films showed a dependence on CuO sintering temperature and on plasma processing time. A stable form of metallic copper, that does not oxidize, was produced at lower sintering temperatures and longer plasma processing times. At other conditions, a metastable form of metallic copper was obtained, which readily transformed to Cu2O. Based on the results, a transformation pathway scheme was elaborated. The scheme can provide with a route to rapidly produce high quality Cu2O films on glass with tunable electrical and optical properties.

Performance Improvement of Solid Oxide Cells Using CuO Sintering Aid for Co-Sintering of GDC Buffer Layer and La0.6Sr0.4Co0.2Fe0.8O3-δ Air Electrode

The effects of a Cu-based additive and nano-Gd-doped ceria (GDC) sol on the sintering temperature for the construction of solid oxide cells (SOCs) were investigated. A GDC buffer layer with 0.25–2 mol% CuO as a sintering aid was prepared by reacting GDC powder and a CuN2O6 solution, followed by heating at 600 °C. The sintering of the CuO-added GDC powder was optimized by investigating linear shrinkage, microstructure, grain size, ionic conductivity, and activation energy at temperatures ranging from 1000 to 1400 °C. The sintering temperature of the CuO–GDC buffer layer was decreased from 1400 °C to 1000 °C by adding the CuO sintering aid at levels exceeding 0.5 mol%. The ionic conductivity of the CuO–GDC electrolyte was maximized at 0.5 mol% CuO. However, the addition of CuO did not significantly affect the activation energy of the GDC buffer layer. Buffer layers with CuO-added GDC or nano-GDC sol-infiltrated GDC were fabricated and tested in co-sintering (1050 °C, air) with La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). In addition, SOC tests were performed using button cells and flat tubular type five-cell stacks. The button cell exhibited the maximum power density of 0.89 W cm−2 in solid oxide fuel cell (SOFC) mode. The stack operated more than 1,000 h in solid oxide electrolysis cell (SOEC) mode.

Effect of CeO2 and CuO sintering additives on the properties of KNN-based piezoelectric ceramics

The 0·95(K0·5Na0·5)NbO3–0·05Ba(Zr0·05Ti0·95)O3-xCeO2/yCuO ceramics were prepared by traditional ceramic method. The effects of sintering additives on the microstructure and electric properties of the ceramics were investigated. The results indicate that CeO2 and CuO additives can lower the sintering temperature and effectively improve the densification and electric properties of the ceramics. CuO is more appropriate than CeO2 as a sintering aid for preparing 0·95(K0·5Na0·5)NbO3–0·06Ba(Zr0·05Ti0·95)O3 ceramics that possess optimum properties: d33 = 82 pC/N, kp = 52%, εr = 1300, tan δ = 0·0208 and Tc = 295 °C.

Characterizations of low-temperature sintered BaCo1.3Ti1.3Fe9.4O19 M-type ferrite for high-frequency antenna application

BaCo1.3Ti1.3Fe9.4O19 ferrite was synthesized by solid-state reaction route. Co and Ti ions were substituted for Fe cation to modify the anisotropy field of the ferrite. The effects of B2O3 and CuO sintering additives on the phase stability, sintering behavior at 900 °C, microstructure development, magnetic and dielectric properties of the ferrite were investigated. The densification of the ferrite at 900 °C was found to increase upon B2O3 and CuO addition. A permittivity of 19 and initial permeability of 11 was obtained in the ferrite containing 5 wt% B2O3 sintering additive. There was a nominal decrease in saturation magnetization of the ferrite with increasing sintering additive. An antenna based on the low temperature sintered ferrite substrate was designed. Antenna parameters such as resonance frequency, return loss, voltage standing wave ratio (VSWR), and bandwidth were simulated and reported. The antenna miniaturization factor (n) was calculated and found n = 11 for the sample with 5 wt% B2O3. The sample containing 3 wt% B2O3 plus 2 wt% CuO showed an impedance of about Zi = 1.

Development of solid oxide cells by co-sintering of GDC diffusion barriers with LSCF air electrode

Abstract The effects of a Cu-based additive and nano-Gd-doped ceria (GDC) sol on the sintering temperature for the construction of solid oxide cells (SOCs) were investigated. A GDC buffer layer with 0.25–2 mol% CuO as a sintering aid was prepared by reacting GDC powder and a CuN2O6 solution, followed by heating at 600 °C. The sintering of the CuO-added GDC powder was optimized by investigating linear shrinkage, microstructure, grain size, ionic conductivity, and activation energy at temperatures ranging from 1000 to 1400 °C. The sintering temperature of the CuO–GDC buffer layer was decreased from 1400 °C to 1100 °C by adding the CuO sintering aid at levels exceeding 0.25 mol%. The ionic conductivity of the CuO–GDC electrolyte was maximized at 0.5 mol% CuO. However, the addition of CuO did not significantly affect the activation energy of the GDC buffer layer. Buffer layers with CuO-added GDC or nano-GDC sol-infiltrated GDC were fabricated and tested in co-sintering (1050 °C, air) with La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). In addition, SOC tests were performed using button cells (active area: 1 cm2) and five-cell (active area: 30 cm2/cell) stacks. The button cell exhibited the maximum power density of 0.89 W cm−2 in solid oxide fuel cell (SOFC) mode. The stack demonstrated more than 1000 h of operation stability in solid oxide electrolysis cell (SOEC) mode (decay rate: 0.004%/kh).

Enhancing magnetoelectric properties of 0–3 particulate composite ceramics by introducing nano-sized sintering aids via self-combustion method

The 0.55Pb(Ni1/3Nb2/3)O3-0.05PbHfO3-0.4PbTiO3/Ni0.875Zn0.125Fe2O4 (PNNHT/NZF) 0–3 particulate composite ceramics were prepared by the conventional solid-state reaction method via introducing the nano-sized WO3 and CuO sintering aids by the self-combustion method. Due to the introducing of nano-sized sintering aids, densified PNNHT/NZF composite ceramics are synthesized sintered at low sintering temperature. Furthermore, the nano-sized sintering aids act effectively as blocking layers, leading to compact composite ceramics with homogenously dispersed and isolated microstructure morphology, inhibiting inter-phase diffusion, avoiding interfacial chemical reaction, and achieving strong inter-phase coupling. Therefore, the synthesized PNNHT/NZF composite ceramics exhibit enhanced magnetoelectric properties.

Low-temperature sintering of K0.5Na0.5NbO3 lead free ceramics using nano CuO sintering aid

Lead free piezoelectric ceramic K0.5Na0.5NbO3 (KNN) was synthesized by conventional mixed oxide method. The effect of nano CuO additive as the sintering aid, on microstructure and electrical properties of pure KNN ceramics was investigated. Sintering process has a great impact on the piezoelectric properties of lead free piezoelectric ceramics. The results indicated that adding small amount of nano CuO sintering aid reduces the sintering temperature of lead free piezoelectric KNN ceramic to 900 °C, and also leads to excellent densification and proper microstructure. Samples characterization by X-ray diffraction represented that there are no secondary phases for KNN ceramics with CuO additive in the range of 0–2 mol%. The dielectric and piezoelectric properties are strongly modified by the amount of nano CuO additive. A high piezoelectric coefficient (d33) up to 130 pC/N and a dielectric loss <0.008 achieved for the sample with 0.5 mol% nano CuO, sintered at 900 °C for 4 h.