MXene fillers and silver flakes filled epoxy resin for new hybrid conductive adhesives

The addition of V₂CT_x two-dimensional materials as auxiliary fillers in conductive adhesives can increase the contact area between conductive particles inside the matrix effectively reducing the resistivity of epoxy resin conductive adhesives. The V₂CT_x/Ag/rGO/MWCNTs fillers inside the epoxy resin will connect more Ag-clad Cu particles to form a conductive pathway, but its excessive content will be aggregated inside and thus increase the resistivity of the conductive adhesive. The volume resistivity of ECAs increases from 4.4 × 10⁻⁶ Ω m to 1.15 × 10⁻⁵ Ω m when the V₂CT_x/Ag/rGO/MWCNTs content of 0.1% increases to 0.34%. The Ag-clad Cu particles are interconnected inside the epoxy resin to form an electron transfer network. Inside the epoxy resin substrate Ag-clad Cu particles and V₂CT_x/Ag/rGO/MWCNTs interconnects to form a larger conductive network, so that the conductive adhesive shows good conductive properties.     

SDS-stabilized graphene nanosheets for highly electrically conductive adhesives

We report sodium dodecyl sulfate (SDS) stabilization of graphene nanosheets, with two different sizes as auxiliary fillers inside the conventional electrically conductive adhesive (ECA) composite. Using this non-covalent modification approach we were able to preserve the single-layer structure of graphene layers and prevent their re-stacking inside the composite, which resulted in a significant electrical conductivity improvement of ECAs at noticeably low filler content. Addition of 1.5 wt% small and large SDS-modified graphene into the conventional ECAs with 10 wt% silver flakes led to low electrical resistivity values of 5.5 × 10³ Ω cm and 35 Ω cm, respectively, while at least 40 wt% of silver flakes was required for the conventional ECA to be electrically conductive. A highly conductive ECA with very low bulk resistivity of 1.6 × 10⁻⁵ Ω cm was prepared by adding 1.5 wt% of SDS-modified large graphene into the conventional ECA with 80 wt% silver flakes which is less than that of eutectic lead-based solders.     

Application of nitrogen-doped graphene nanosheets in electrically conductive adhesives

Nitrogen-doped graphene nanosheets (N-GNSs) were used as a conductive filler for a polymer resin adhesive and as a performance improver for a silver-filled electrically conductive adhesive (ECA). The N-GNS samples were prepared by the chemical-intercalation/thermal-exfoliation of graphite followed by a thermal treatment in NH₃. Only 1 wt.% of N-GNSs was required for the adhesive to reach a percolation threshold, and the performance using N-GNSs was much better than that obtained using carbon black or multi-walled carbon nanotubes (MWCNTs). The effect of N-GNS or MWCNT additives on reducing the electrical resistivity of Ag-particle filled ECAs at low Ag loading ratios was also investigated. With 30 wt.% of Ag filler, the polymer resin was still non-conducting, while a resistivity of 4.4 × 10⁻² Ω-cm was obtained using an Ag/N-GNS hybrid filler fortified with only 1 wt.% of N-GNSs due to large specific surface area, high aspect ratio, and good electrical conductivity of the doped graphene.     

Electrically conductive SiC ceramics processed by pressureless sintering

Polycrystalline SiC ceramics with 10 vol% Y₂O₃-AlN additives were sintered without any applied pressure at temperatures of 1900-2050°C in nitrogen. The electrical resistivity of the resulting SiC ceramics decreased from 6.5 × 10¹ to 1.9 × 10⁻² Ω·cm as the sintering temperature increased from 1900 to 2050°C. The average grain size increased from 0.68 to 2.34 μm with increase in sintering temperature. A decrease in the electrical resistivity with increasing sintering temperature was attributed to the grain-growth-induced N-doping in the SiC grains, which is supported by the enhanced carrier density. The electrical conductivity of the SiC ceramic sintered at 2050°C was ~53 Ω⁻¹·cm⁻¹ at room temperature. This ceramic achieved the highest electrical conductivity among pressureless liquid-phase sintered SiC ceramics.     

Improving the electrical properties of niobium-doped titania sputtering targets by sintering in oxygen-deficient atmospheres

Niobium-doped titania (TNO) film can be used as a transparent conductive oxide (TCO) film due to its excellent conductivity and visible transparency. The performances of TNO sputtering targets are thus critical issues in optimizing sputtered films. This study clarifies the influences of inert and reducing atmospheres on the microstructure, densification, crystal structure, and electrical properties of TNO sputtering targets. The results indicate that a sintering atmosphere of 90% Ar–10% H₂ can result in a lower sintered density, larger grain size, and lower resistivity than can an atmosphere of Ar, followed by one of air. Sintering in 90% Ar–10% H₂ or Ar obviously decreases the resistivity of TiO₂, from >10⁸ Ω cm to <10⁻¹ Ω cm, and the TNO target, from >10¹ Ω cm to <10⁻¹ Ω cm. The resistivity of TNO target sintered at 1200 °C in 90% Ar–10% H₂ is as low as 1.8×10⁻² Ω cm.     

Effect of Ni content and its particle size on electrical resistivity and flexural strength of porous SiC ceramic sintered at low-temperature using clay additive

A low-temperature sintered porous SiC-based clay-Ni system with controlled electrical resistivity (2.54 × 10¹⁰ Ω cm to 2 Ω cm), and thermal conductivity (3.5 W/m. K to 12.6 W/m. K) was successfully designed. Clay (20 wt% kaolin) was used as a sintering additive in all the compositions. The electrical resistivity, and thermal conductivity was controlled by varying the Ni content (0–25 wt%) in the samples. The electrical resistivity was recorded as low as 2 Ω cm with 25 wt% Ni that was sintered at 1400 °C in argon. The interface reaction between Ni and SiC formed conductive nickel silicide (Ni₂Si), while the transformation of kaolin to mullite strengthened the mechanical properties. Submicron-sized Ni (0.3 μm) was more effective than micron-sized Ni (3.5 μm) in reducing the electrical resistivity, and increasing the thermal conductivity along with flexural strength. A comparative study of sintering temperatures showed that 1400 °C resulted in the lowest electrical resistivity (2 Ω cm) and the highest thermal conductivity of 12.6 W/m. K with flexural strength of 54 MPa at 32% porosity in the SiC-kaolin-Ni system.     

Study of processing variables on the electrical resistivity of conductive adhesives

In this paper, the authors explored the effects of processing variables, including carbon nanotube (CNT) concentration, assembly pressure, and processing temperature, on electrical conductivity of CNT-included electrically conductive adhesives (ECAs). The main effects of these variables were analyzed under specific range for each variable. Response surface methodology was used to investigate the cross-effects of these variables on ECA conductivity. By fitting the experimental data to the response function, minimum bulk resistivity of 1.5×10^?4 Ω cm was obtained at the optimum settings of processing variables (CNT concentration 2%, processing temperature 199 °C, pressure 6000 psi).     

Novel thermal-sensitive properties of NBT-BZT composite ceramics for high-temperature NTC thermistors

We found for the first time that (1 − x) Na_0.5Bi_0.5TiO₃-xBiZn_0.5Ti_0.5O₃ (NBT–BZT) composite ceramics showed negative temperature coefficient (NTC) at a high temperature. The NBT–BZT nanopowders were successfully prepared by Pechini method. Their ceramics were sintered at 1100°C. The NBT–BZT ceramic exhibited a good linear relationship between logarithm of electrical resistivity (Inρ) and reciprocal of absolute temperature (1000/T) at 250°C–1050°C. The obtained ρ₆₀₀, ρ₉₀₀, and B_600/900 constants of the NBT–ZBT NTC thermistors are approximately 5.92 × 10⁶ to 3.01 × 10⁴ Ω cm, 7.03 × 10³ to 7.60 × 10² Ω cm and 2.3 × 10⁴-1.3 × 10⁴ K, respectively. The electrical characteristics can be tuned to the desired value by changing the Na_0.5Bi_0.5TiO₃ content in the compound. The electrical conductivity in these compounds is due to the electron jumps between Ti³⁺ and Ti⁴⁺ and oxygen-ion conductivity. Results demonstrate a tremendous potential of the studied system for perovskite materials with NTC performance.     

Microstructural,electrical, and mechanical properties of conductive SiC ceramics fabricated by spark plasma sintering

Nitrogen (N)-doped conductive silicon carbide (SiC) of various electrical resistivity grades can satisfy diverse requirements in engineering applications. To understand the mechanisms that determine the electrical resistivity of N-doped conductive SiC ceramics during the fast spark plasma sintering (SPS) process, SiC ceramics were synthesized using SPS in an N₂ atmosphere with SiC powder and traditional Al₂O₃–Y₂O₃ additive as raw materials at a sintering temperature of 1850–2000°C for 1–10 min. The electrical resistivity was successfully varied over a wide range of 10⁻³–10¹ Ω cm by modifying the sintering conditions. The SPS-SiC ceramics consisted of mainly Y–Al–Si–O–C–N glass phase and N-doped SiC. The Y–Al–Si–O–C–N glass phase decomposed to an Si-rich phase and N-doped Y_xSi_yC_z at 2000°C. The Vickers hardness, elastic modulus, and fracture toughness of the SPS-SiC ceramics varied within the ranges of 14.35–25.12 GPa, 310.97–400.12 GPa, and 2.46–5.39 MPa m^1/2, respectively. The electrical resistivity of the obtained SPS-SiC ceramics was primarily determined by their carrier mobility.     

Highly conductive SiC ceramics containing Ti2CN

Highly conductive SiC ceramics were fabricated by sintering β-SiC and TiN powder mixture in N₂ atmosphere. SiC ceramics exhibited decreased electrical resistivity (ρ) with increasing TiN content. X-ray diffraction data indicated that the specimens consisted of β-SiC grains without a detectible secondary phase for low TiN content (≤2 vol%) but contained a Ti₂CN phase as the TiN content increased. The temperature-dependent resistivity ρ(T) of specimens revealed semiconductor-like behavior for TiN content up to 10 vol% and metal-like behavior above 20 vol%. For the specimen with TiN content of 15 vol%, ρ(T) remained almost constant (2.06 ± 0.01 × 10⁻³ Ω cm) in the 4–300 K range. The resistivity of metal-like specimens were as low as 3.5 × 10⁻⁴ Ω cm for TiN content of 20 vol%. For semiconductor-like specimens, ρ(T) was primarily affected by N donors in the β-SiC grains. Metal-like specimens were primarily affected by metallic Ti₂CN clusters.     

Thermal and electrical properties of additive-free rapidly hot-pressed SiC ceramics

The thermal and electrical properties of newly developed additive free SiC ceramics processed at a temperature as low as 1850 °C (RHP0) and SiC ceramics with 0.79 vol.% Y₂O₃-Sc₂O₃ additives (RHP79) were investigated and compared with those of the chemically vapor-deposited SiC (CVD-SiC) reference material. The additive free RHP0 showed a very high thermal conductivity, as high as 164 Wm⁻¹ K⁻¹, and a low electrical resistivity of 1.2 × 10⁻¹ Ω cm at room temperature (RT), which are the highest thermal conductivity and the lowest electrical resistivity yet seen in sintered SiC ceramics processed at ≤1900 °C. The thermal conductivity and electrical resistivity values of RHP79 were 117 Wm⁻¹ K⁻¹ and 9.5 × 10⁻² Ω cm, respectively. The thermal and electrical conductivities of CVD-SiC parallel to the direction of growth were ∼324 Wm⁻¹ K⁻¹ and ∼5 × 10⁻⁴Ω⁻¹ cm⁻¹ at RT, respectively.     

Large enhancement of piezoelectric properties and resistivity in Cu/Ta co-doped Bi4Ti3O12 high-temperature piezoceramics

In this study, the electrical properties of Bi₄Ti₃O₁₂-based Aurivillius-type ceramics were tailored by a B-site co-doping strategy combining high valence Ta⁵⁺ and low valence Cu²⁺. A series of Bi₄Ti_3−x(Cu_1/3Ta_2/3)_xO₁₂ (BTCT) (x = 0, 0.005, 0.01, 0.015, 0.02, 0.025, and 0.03) ceramics were prepared by the conventional solid-state reaction method. The effect of Cu/Ta co-doping on the crystal structure, microstructure, dielectric properties, piezoelectric properties, ferroelectric properties, and electrical conductivity of these ceramics was systematically investigated. Co-doping significantly enhanced the piezoelectric properties and DC electrical resistivity of the resulting composites. The optimized comprehensive performances were obtained at x = 0.015 with a large piezoelectric coefficient (34 pC/N) and a relatively high resistivity of 9.02 × 10⁶ Ω cm at 500°C. Furthermore, the ceramic also exhibited stable thermal annealing behaviors and excellent fatigue resistance. The results of this study demonstrated great potential of the Cu/Ta co-doped Bi₄Ti₃O₁₂ ceramics for high-temperature piezoelectric device applications.     

Synthesis and performance of TiB2–B4C composites by high pressure of TiC–B mixture

TiB₂–B₄C composites were in situ synthesized and consolidated by high pressure synthesis method from a mixture of TiC and B powders at the pressure and temperature of 5.0 GPa and 1500℃-1900℃. The phase composition, microstructure, density, hardness, thermal conductivity, and electrical resistivity of TiB₂–B₄C composites were analyzed. As the increase in the synthesis temperature, the products were TiB₂ and B₄C phases and that crystallinity improved. TiB₂–B₄C composites were dense without obvious pores. TiB₂–B₄C composites synthesized at 1800℃ obtained the optimized performance, including the relative density of 98.2%, the Vickers hardness of 31.7 ± 1.2 GPa with the load of 9.8 N, the thermal conductivity of 30.3 ± 0.7 W/(m K), and the electrical resistivity of 3.3 × 10⁻³ Ω cm, respectively. The grain size of the TiB₂–B₄C composites changed with the increase in synthesis temperature, leading to the changes in hardness, thermal conductivity, and electrical resistivity.     

Electrical and mechanical properties of pressureless sintered SiC-Ti2CN composites

Highly conductive SiC-Ti₂CN composites were fabricated from β-SiC and TiN powders with 10?vol% Y₂O₃-AlN additives via pressureless sintering. The effect of initial TiN content on the microstructure, and electrical and mechanical properties of the SiC-Ti₂CN composites was investigated. It was found that all specimens could be sintered to ≥98% of the theoretical density. The electrical resistivity of the SiC-Ti₂CN composites decreased with increasing initial TiN content. The SiC-Ti₂CN composites prepared from 25?vol% TiN showed the highest electrical conductivity (～1163 (Ω?cm)^?1) for any pressureless sintered SiC ceramics thus far. The high electrical conductivity of the composites was attributed to the in situ-synthesis of an electrically conductive Ti₂CN phase and the growth of N-doped SiC grains during pressureless sintering. The flexural strength, fracture toughness, and Vickers hardness of the composite fabricated with 25?vol% TiN were 430?MPa, 4.9?MPa?m^1/2, and 23.1?GPa, respectively, at room temperature.     

Preparation and characterization of transparent indium- doped TiO2 films deposited by MOCVD

Titanium dioxide (TiO₂) films doped with different indium (In) concentrations have been prepared on SrTiO₃ (STO) substrates by high vacuum metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) analyses revealed the TiO₂ films doped with low In concentrations to be [001] oriented anatase phase and the films with high In concentrations to present polycrystalline structures. The 1.8% In-doped TiO₂ film exhibited the best electrical conductivity properties with the lowest resistivity of 8.68×10⁻² Ω cm, a Hall mobility of 10.9 cm² V⁻¹ s⁻¹ and a carrier concentration of 6.5×10¹⁸ cm⁻³. The films showed excellent transparency with average transmittances of over 85% in the visible range.     

Electrical and Thermal Properties of SiC Ceramics Sintered with Yttria and Nitrides

The electrical and thermal properties of SiC ceramics containing 1 vol% nitrides (BN, AlN or TiN) were investigated with 2 vol% Y₂O₃ addition as a sintering additive. The AlN‐added SiC specimen exhibited an electrical resistivity (3.8 × 10¹ Ω·cm) that is larger by a factor of ~10² compared to that (1.3 × 10^?1 Ω·cm) of a baseline specimen sintered with Y₂O₃ only. On the other hand, BN‐ or TiN‐added SiC specimens exhibited resistivity that is lower than that of the baseline specimen by a factor of 10^?1. The addition of 1 vol% BN or AlN led to a decrease in the thermal conductivity of SiC from 178 W/m·K (baseline) to 99 W/m·K or 133 W/m·K, respectively. The electrical resistivity and thermal conductivity of the TiN‐added SiC specimen were 1.6 × 10^?2 Ω·cm and 211 W/m·K at room temperature, respectively. The present results suggest that the electrical and thermal properties of SiC ceramics are controllable by adding a small amount of nitrides.     

The Sintering Trajectory and Electrical Properties of Niobium‐Doped Titania Sputtering Targets

Nb‐doped TiO₂ (TNO) films, which are highly conductive and transparent, can be used as transparent conductive oxide (TCO) films. A predominant manufacturing method for TCO film is magnetron sputtering, and the material of the sputtering target affects the performance of the film. The objective of this study was to investigate the sintering densification, microstructure, and electrical properties of TNO and TiO₂ sputtering targets. The results showed that the segregation of Nb at the grain boundary in TNO helps to facilitate densification and inhibit grain growth. After 1200°C sintering, the sintered density of TNO target achieves almost 100% of the theoretical density. Moreover, the Nb₂O₅ additive greatly improves the electrical properties, decreasing the resistivity of TiO₂ from >10⁸ Ωcm to 4.6 × 10¹ Ωcm. Correlations between TNO sputtering target investigated in this study and TNO sputtered film reported in the literature are also preliminarily established. The resistivity of TNO film with an anatase structure is obviously lower than that of TNO target with a rutile structure.     

Electrically conductive SiC–(Nb,Ti)ss–(Nb,Ti)Css cermet

The present paper deals with the processing method of SiC–(Nb,Ti)_(ss)–(Ti,Nb)C_(ss) composites. The electrically conductive phases were formed by in situ reaction: NbC_(s) + Ti_(s) → (Nb,Ti)_(ss) + (Ti,Nb)C_(ss) that takes place during the reaction sintering by hot pressing. Prepared composites exhibit good compromise between electrical and mechanical properties and the present approach allows preparing a wide variety of compositions. For example composites containing 80 wt.% SiC and 20 wt.% {(Nb,Ti)_(ss)–(Ti,Nb)C_(ss)} have an electrical resistivity 2.6 × 10⁻⁴ Ω m, hardness 21.6 GPa and fracture toughness 6.3 MPa m^1/2.     

Structure and lithium-ion mobility in Li1.5M0.5Ge1.5(PO4)3 (M = Ga,Sc, Y) NASICON glass-ceramics

This work reports structural and lithium-ion mobility studies in NASICON single- or multiple phase Li_1+xM_xGe_2−x(PO₄)₃ (M = Ga³⁺, Sc³⁺, Y³⁺) glass-ceramics using solid-state NMR techniques, X-ray powder diffraction, and impedance spectroscopy. X-ray powder diffraction data show the successful incorporation of Ga³⁺ and Sc³⁺ into the Ge⁴⁺ octahedral sites of the NASICON structure at the levels of x = 0.5 and 0.4, respectively. The glass-to-crystal transition was further characterized by multinuclear NMR and electrical conductivity measurements. Among the studied samples, the gallium-containing glass-ceramic presented the highest DC conductivity, 1.1 × 10⁻⁴ S/cm at room temperature, whereas for the Sc-containing samples, the maximum room temperature conductivity that could be reached was 4.8 × 10⁻⁶ S/cm. No indications of any substitution of Ge⁴⁺ by Y³⁺ could be found.