Effects of Nb Content on the Ferroelectric and Dielectric Properties of Nb/Nd-Co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films

Nd/Nb-co-substituted Bi_3.15Nd_0.85Ti_3?x Nb _x O₁₂ (BNTN _x , x = 0.01, 0.03, 0.05 and 0.07) thin films were grown on Pt/Ti/SiO₂/Si (100) substrates by chemical solution deposition. The effects of Nb content on the micro-structural, dielectric, ferroelectric, leakage current and capacitive properties of the BNTN _x thin films were investigated. A low-concentration substitution with Nb ions in BNTN _x can greatly enhance its remanent polarization (2P _r) and reduce the coercive field (2E _c) compared with those of Bi₄Ti₃O₁₂ (BIT) thin film. The highest 2P _r (71.4 μC/cm²) was observed in the BNTN_0.03 thin film when the 2E _c was 202 kV/cm. Leakage currents of all the films were on the order of 10^?6 to 10^?5 A/cm², and the BNTN_0.03 thin film has a minimum leakage current (2.1 × 10^?6 A/cm²) under the high electric field (267 kV/cm). Besides, the C–V curve of the BNTN_0.03 thin film is the most symmetrical, and the maximum tunability (21.0%) was also observed in this film. The BNTN_0.03 thin film shows the largest dielectric constant and the lowest dielectric loss and its maximum Curie temperature is 410 ± 5°C.     

Microwave Dielectric Properties of BiCu<Subscript>2</Subscript>PO<Subscript>6</Subscript> Ceramics with Low Sintering Temperature

A BiCu₂PO₆ microwave dielectric ceramic was prepared using a solid-state reaction method. As the sintering temperature increased from 800°C to 880°C, the bulk density of BiCu₂PO₆ ceramic increased from 6.299 g/cm³ to 6.366 g/cm³; the optimal temperature was 860°C. The best microwave dielectric properties [permittivity (? _r ) = ～16, a quality factor (Q × f) = ～39,110 GHz and a temperature coefficient of resonant frequency (τ _f ) = ～?59 ppm/°C] were obtained in the ceramic sintered at 860°C for 2 h. Then, TiO₂ with a positive τ _f (～+400 ppm/°C) was added to compensate the τ _f value. The composite material was found to have a near-zero τ _f (+2.7 ppm/°C) and desirable microwave properties (? _r  = 19.9, Q × f = 24,885 GHz) when synthesized at a sintering temperature of 880°C. This system could potentially be used for low-temperature co-fired ceramics technology applications.     

Influence of Indium-Tin Oxide Additive on the Sintering Process and Conductivity of Na<Subscript>3</Subscript>Zr<Subscript>2</Subscript>Si<Subscript>2</Subscript>PO<Subscript>12</Subscript> Solid Electrolyte

Because of the poor sintering ability and low phase purity limit in the application of a Na₃Zr₂Si₂PO₁₂ solid electrolyte, it is important to find an effective way to obtain a pure and dense Na₃Zr₂Si₂PO₁₂ ceramic at reduced temperature. In this study, high conductive indium-tin oxide (ITO) was innovatively used as the sintering additive to improve the purity and density of the Na₃Zr₂Si₂PO₁₂ ceramic. The influence of ITO additive on density, phase, microstructure and conductivity of the Na₃Zr₂Si₂PO₁₂ ceramic was investigated. Archimedes method, x-ray diffraction, scanning electron microcopy and complex impedance spectroscopy were used as experimental techniques to evaluate the effect of the additive. The results show that the ITO sintering additive increases not only the purity and density but also the conductivity of the Na₃Zr₂Si₂PO₁₂ ceramic. The Na₃Zr₂Si₂PO₁₂ ceramic with 3 wt.% ITO additive sintered at 1150°C for 4 h possesses a high density of 3.15 g/cm³ and good conductivity of (3.95 ± 0.12) × 10^?4 S/cm.     

Effect of ZnO Nanoparticles on the Sintering Behavior and Physical Properties of Bi<Subscript>0.5</Subscript>(Na<Subscript>0.8</Subscript>K<Subscript>0.2</Subscript>)<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> Lead-Free Ceramics

Sintered Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ + x wt.% ZnO nanoparticle (BNKT–xZnO_n) ceramics have been fabricated by conventional annealing with the aid of ultrasound waves for preliminary milling. Because of the presence of the liquid Bi₂O₃–ZnO phase at the eutectic point of 738°C, the sintering temperature decreased from 1150°C to 1000°C, and the morphology phase boundary of BNKT–xZnO_n ceramics can be clarified by two separated peaks at (002)_T and (200)_T of 2θ in the x-ray diffraction (XRD) patterns. The improvement of ferroelectric properties has been obtained for BNZT–0.2 wt.% ZnO_n ceramics by the increase of remanent polarization up to 20.4 μC/cm² and a decrease of electric coercive field down to 14.2 kV/cm. The piezoelectric parameters of the ceramic included a piezoelectric charge constant of d ₃₁ = 78 pC/N; electromechanical coupling factors k _p = 0.31 and k _t = 0.34, larger than the values of 42 pC/N, 0.12 and 0.13, respectively, were obtained for the BNKT ceramics.     

Charge carrier transport in Ge<Subscript>20</Subscript>As<Subscript>20</Subscript>S<Subscript>60</Subscript> chalcogenide semiconductor films

Charge-carrier transport in Ge₂₀As₂₀S₆₀ films has been studied using the transit time method under low-injection conditions at room temperature. It was found that drift mobilities of electrons and holes in Ge₂₀As₂₀S₆₀ films are close to each other, i.e., μ _e ≈ μ _h ≈ 2 × 10⁻³ cm² V⁻¹ s⁻¹ at T = 295 K and F = 5 × 10⁴ V/cm. It was shown that the time dependence of the photocurrent during carrier drift and the voltage dependence of the drift mobility allowed the use of the concept of anomalous dispersive transport. Experimental data were explained using the model of transport controlled by carrier trapping by localized states with energy distribution near conduction and valence band edges described by the exponential law with a characteristic energy of ∼0.05 eV.     

Evaluation of Pd Nanoparticle-Decorated CeO<Subscript>2</Subscript>-MWCNT Nanocomposite as an Electrocatalyst for Formic Acid Fuel Cells

In this work, CeO₂-modified Pd/CeO₂-carbon nanotube (CNT) electrocatalyst for the electro-oxidation of formic acid has been investigated. The support CNT was first modified with different amounts (5–30 wt.%) of CeO₂ using a precipitation-deposition method. The electrocatalysts were developed by dispersing Pd on the CeO₂-CNT supports using the borohydride reduction method. The synthesized electrocatalysts were analyzed for composition, morphology and electronic structure using x-ray diffraction (XRD), scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) techniques. The formation of Pd nanoparticles on the CeO₂-CNT support was confirmed using TEM. The activity of Pd/CeO₂-CNT and of Pd-CNT samples upon oxidation of formic acid was evaluated by using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry. The addition of moderate amounts of cerium oxide (up to 10 wt.%) significantly improved the activity of Pd/CeO₂-CNT compared to the unmodified Pd-CNT. Pd/10 wt.% CeO₂-CNT showed a current density of 2 A mg^?1, which is ten times higher than that of the unmodified Pd-CNT (0.2 A mg^?1). Similarly, the power density obtained for Pd/10 wt.% CeO₂-CNT in an air-breathing formic acid fuel cell was 6.8 mW/cm² which is two times higher than Pd-CNT (3.2 mW/cm²), thus exhibiting the promotional effects of CeO₂ to Pd/CeO₂-CNT. A plausible justification for the improved catalytic performance and stability is provided in the light of the physical characterization results.     

Structural and Electrical Properties of Ag/<Emphasis Type="Italic">n</Emphasis>-TiO<Subscript>2</Subscript>/<Emphasis Type="Italic">p</Emphasis>-Si/Al Heterostructure Fabricated by Pulsed Laser Deposition Technique

We have investigated the structural and electrical characteristics of the Ag/n-TiO₂/p-Si/Al heterostructure. Thin films of pure TiO₂ were deposited on p-type silicon (100) by optimized pulsed laser ablation with a KrF-excimer laser in an oxygen-controlled environment. X-ray diffraction analysis showed the formation of crystalline TiO₂ film having a tetragonal texture with a strong (210) plane as the preferred direction. High purity aluminium and silver metals were deposited to obtain ohmic contacts on p-Si and n-TiO₂, respectively. The current–voltage (I–V) characteristics of the fabricated heterostructure were studied by using thermionic emission diffusion mechanism over the temperature range of 80–300 K. Parameters such as barrier height and ideality factor were derived from the measured I–V data of the heterostructure. The detailed analysis of I–V measurements revealed good rectifying behavior in the inhomogeneous Ag/n-TiO₂/p-Si(100)/Al heterostructure. The variations of barrier height and ideality factor with temperature and the non-linearity of the activation energy plot confirmed that barrier heights at the interface follow Gaussian distributions. The value of Richardson’s constant was found to be 6.73 × 10⁵ Am^?2 K^?2, which is of the order of the theoretical value 3.2 × 10⁵ Am^?2 K^?2. The capacitance–voltage (C–V) measurements of the heterostructure were investigated as a function of temperature. The frequency dependence (Mott–Schottky plot) of the C–V characteristics was also studied. These measurements indicate the occurrence of a built-in barrier and impurity concentration in TiO₂ film. The optical studies were also performed using a UV–Vis spectrophotometer. The optical band gap energy of TiO₂ films was found to be 3.60 eV.     

Effect of Annealing Temperature on Flowerlike Cu<Subscript>3</Subscript>BiS<Subscript>3</Subscript> Thin Films Grown by Chemical Bath Deposition

For widespread application of thin-film photovoltaic solar cells, synthesis of inexpensive absorber material is essential. In this work, deposition of ternary Cu₃BiS₃ absorber material, which contains abundant and environmentally benign elements, was carried out on glass substrate. Flowerlike Cu₃BiS₃ thin films with nanoflakes as building block were formed on glass substrate by chemical bath deposition. These films were annealed at 573 K and 673 K in sulfur ambient for structural improvement. Their structure was characterized using Raman spectroscopy, as well as their surface morphological and optical properties. The x-ray diffraction profile of as-deposited Cu₃BiS₃ thin film revealed amorphous structure, which transformed to orthorhombic phase after annealing. The Raman spectrum exhibited a characteristic peak at 290 cm^?1. Scanning electron microscopy of as-deposited Cu₃BiS₃ film confirmed formation of nanoflowers with diameter of around 1052 nm. Wettability testing of as-deposited Cu₃BiS₃ thin film demonstrated hydrophobic nature, which became hydrophilic after annealing. The measured ultraviolet–visible (UV–Vis) absorption spectra of the Cu₃BiS₃ thin films gave an absorption coefficient of 10⁵ cm^?1 and direct optical bandgap of about 1.42 eV after annealing treatment. Based on all these results, such Cu₃BiS₃ material may have potential applications in the photovoltaic field as an absorber layer.     

Optical Properties of K<Subscript>2</Subscript>O-Li<Subscript>2</Subscript>O-WO<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Glasses: Evidence of Mixed Alkali Effect

Glass with compositions xK₂O-(30 ? x)Li₂O-10WO₃-60B₂O₃ for 0 ≤ x ≤ 30 mol.% have been prepared using the normal melt quenching technique. The optical reflection and absorption spectra were recorded at room temperature in the wavelength range 300–800 nm. From the absorption edge studies, the values of the optical band gap (E _opt) and Urbach energy (ΔE) have been evaluated. The values of E _opt and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple Di-Domenico model.     

Dielectric,Impedance and Conduction Behavior of Double Perovskite Pr<Subscript>2</Subscript>CuTiO<Subscript>6</Subscript> Ceramics

Polycrystalline Pr₂CuTiO₆ (PCT) ceramics exhibits dielectric, impedance and modulus characteristics as a possible material for microelectronic devices. PCT was synthesized through the standard solid-state reaction method. The dielectric permittivity, impedance and electric modulus of PCT have been studied in a wide frequency (100 Hz–1 MHz) and temperature (303–593 K) range. Structural analysis of the compound revealed a monoclinic phase at room temperature. Complex impedance Cole–Cole plots are used to interpret the relaxation mechanism, and grain boundary contributions towards conductivity have been estimated. From electrical modulus formalism polarization and conductivity relaxation behavior in PCT have been discussed. Normalization of the imaginary part of impedance (Z″) and the normalized imaginary part of modulus (M″) indicates contributions from both long-range and localized relaxation effects. The grain boundary resistance along with their relaxation frequencies are plotted in the form of an Arrhenius plot with activation energy 0.45 eV and 0.46 eV, respectively. The ac conductivity mechanism has been discussed.     

The TiO<Subscript>2</Subscript> Hierarchical Structure with Nanosheet Spheres for Improved Photoelectric Performance in Dye-Sensitized Solar Cells

A bi-layer photoanode is successfully fabricated for dye-sensitized solar cells (DSSCs) composed of P25/TiO₂ nanorod (P25/TNR) as the underlayer and TiO₂ nanosheet spheres (TNSs) as the light-scattering layer. Notably, the P25-TNR provides multiple functions, including more dye loading, more efficient charge transport and a lower electron recombination rate for the photoanode. Besides, the unique structure of TNS can significantly improve the light-harvesting capacity, boosting the light-harvesting efficiency. Therefore, an enhanced short-circuit current and power conversion efficiency of 18.04 mA cm^?2 and 5.99%, respectively, were achieved for the P25/TNR-TNS-based DSSC, which was better than that of the P25-TNS-based (15.17 mA cm^?2, 5.36%) and bare TNS-based (11.43 mA cm^?2, 4.14%) DSSCs. This indicates that this bi-layer structure effectively combines the advantages of the one-dimensional (1D) nanostructure and three-dimensional (3D) hierarchical structure. In short, this work demonstrates the possibility of fabricating desirable photoanodes for high-performance DSSCs by rational design of nanostructures and effective combination of multi-functional components.     

First-Principles Study of Structural,Electronic, Optical,and Thermal Properties of BeSiSb<Subscript>2</Subscript> and MgSiSb<Subscript>2</Subscript>

Structural, electronic, optical, and thermal properties of ternary II–IV–V₂ (BeSiSb₂ and MgSiSb₂) chalcopyrite semiconductors have been calculated using the full-potential linearized augmented plane wave scheme?in the generalized gradient approximation. The optimized equilibrium structural parameters (a, c, and u) are in good agreement with theoretical results obtained using other methods. The band structure and density of states reveal that BeSiSb₂ has an indirect (Γ–Z) bandgap of about 0.61 eV, whereas MgSiSb₂ has a direct (Γ–Γ) bandgap of 0.80 eV. The dielectric function, refractive index, and extinction coefficient were calculated to investigate the optical properties, revealing that BeSiSb₂ and MgSiSb₂ present very weak birefringence. The temperature dependence of the volume, bulk modulus, Debye temperature, and heat capacities (C _v and C _p) was predicted using the quasiharmonic Debye model at different pressures. Significant differences in properties are observed at high pressure and high temperature. We predict that, at 300 K and 0 GPa, the heat capacity at constant volume C _v, heat capacity at constant pressure C _P, Debye temperature θ _D, and Grüneisen parameter γ will be about 94.91 J/mol K, 98.52 J/mol K, 301.30 K, and 2.11 for BeSiSb₂ and about 96.08 J/mol K, 100.47 J/mol K, 261.38 K, and 2.20 for MgSiSb₂, respectively.     

Biosensor properties of SOI nanowire transistors with a PEALD Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dielectric protective layer

The properties of protective dielectric layers of aluminum oxide Al₂O₃ applied to prefabricated silicon-nanowire transistor biochips by the plasma enhanced atomic layer deposition (PEALD) method before being housed are studied depending on the deposition and annealing modes. Coating the natural silicon oxide with a nanometer Al₂O₃ layer insignificantly decreases the femtomole sensitivity of biosensors, but provides their stability in bioliquids. In deionized water, transistors with annealed aluminum oxide are closed due to the trapping of negative charges of <(1–10) × 10¹¹ cm^?2 at surface states. The application of a positive potential to the substrate (V_sub > 25 V) makes it possible to eliminate the negative charge and to perform multiple measurements in liquid at least for half a year.     

Surface texture of single-crystal silicon oxidized under a thin V<Subscript>2</Subscript>O<Subscript>5</Subscript> layer

The process of surface texturing of single-crystal silicon oxidized under a V₂O₅ layer is studied. Intense silicon oxidation at the Si–V₂O₅ interface begins at a temperature of 903 K which is 200 K below than upon silicon thermal oxidation in an oxygen atmosphere. A silicon dioxide layer 30–50 nm thick with SiO₂ inclusions in silicon depth up to 400 nm is formed at the V₂O₅–Si interface. The diffusion coefficient of atomic oxygen through the silicon-dioxide layer at 903 K is determined (D ≥ 2 × 10^–15 cm² s^–1). A model of low-temperature silicon oxidation, based on atomic oxygen diffusion from V₂O₅ through the SiO₂ layer to silicon, and SiO _x precipitate formation in silicon is proposed. After removing the V₂O₅ and silicon-dioxide layers, texture is formed on the silicon surface, which intensely scatters light in the wavelength range of 300–550 nm and is important in the texturing of the front and rear surfaces of solar cells.     

Modified Interface Properties of Au/<Emphasis Type="Italic">n</Emphasis>-type GaN Schottky Junction with a High-<Emphasis Type="Italic">k</Emphasis> Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> Insulating Layer

The interface properties of a Au/n-GaN Schottky junction (SJ) were modified by placing a high-k barium strontium titanate (Ba_0.6Sr_0.4TiO₃) insulating layer between the Au and n-GaN semiconductor. The surface morphology, chemical composition, and electrical properties of Au/Ba_0.6Sr_0.4TiO₃ (BST)/n-GaN metal/insulator/semiconductor (MIS) junctions were explored by atomic force microscopy, energy-dispersive x-ray spectroscopy, current–voltage (I–V) and capacitance–voltage (C–V) techniques. The electrical results of the MIS junction are correlated with the SJ and discussed further. The MIS junction exhibited an exquisite rectifying nature compared to the SJ. An average barrier height (BH) and ideality factors were extracted to be 0.77 eV, 1.62 eV and 0.92 eV, 1.95 for the SJ and MIS junction, respectively. The barrier was raised by 150 meV for the MIS junction compared to the MS junction, implying that the BH was effectively altered by the BST insulating layer. The BH values extracted by I–V, Cheung’s and Norde functions were nearly equal to one another, indicating that the techniques applied here were dependable and suitable. The frequency-dependent properties of the SJ and MIS junction were explored and discussed. It was found that the interface state density of the MIS junction was smaller than the SJ. This implies that the BST layer plays an imperative role in the decreased N_SS. Poole–Frenkel emission was the prevailed current conduction mechanism in the reverse-bias of both the SJ and MIS junction.     

Solvent-Based Synthesis of <Emphasis Type="Italic">Nano</Emphasis>-Bi<Subscript>0.85</Subscript>Sb<Subscript>0.15</Subscript> for Low-Temperature Thermoelectric Applications

In this study we show a preparation method for nanostructured Bi_0.85Sb_0.15 powders via a chemical reduction route in a polyol medium, yielding material with particle sizes of 20–150 nm in scalable amounts. The powders were consolidated by spark plasma sintering (SPS) in order to maintain the nanostructure. To investigate influence of the sinter process, the powders were characterized by x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), and scanning electron microscopy (SEM) measurements before and after SPS. Transport properties, Seebeck effect, and thermal conductivity were determined in the low temperature range below 300 K. The samples showed excellent thermal conductivity of 2.3–2.6 W/m × K at 300 K and Seebeck coefficients from ?97 μV/K to ?107 μV/K at 300 K with a maximum of ?141 μV/K at 110 K, thus leading to ZT values of up to 0.31 at room temperature. The results show that Bi-Sb-alloys are promising materials for low-temperature applications. Our wet chemical approach gives access to scalable amounts of nano-material with increased homogeneity and good thermoelectric properties after SPS.     

Theoretical Study of Electronic Structure and Thermoelectric Properties of Doped CuAlO<Subscript>2</Subscript>

The doping level dependence of thermoelectric properties of delafossite CuAlO₂ has been investigated in the constant scattering time (τ) approximation, starting from the first principles of electronic structure. In particular, the lattice parameters and the energy band structure were calculated using the total energy plane-wave pseudopotential method. It was found that the lattice parameters of CuAlO₂ are a = 2.802 Å and c = 16.704 Å, and the internal parameter is u = 0.1097. CuAlO₂ has an indirect band gap of 2.17 eV and a direct gap of 3.31 eV. The calculated energy band structures were then used to calculate the electrical transport coefficients of CuAlO₂. By considering the effects of doping level and temperature, it was found that the Seebeck coefficient S(T) increases with increasing acceptor doping (A _d) level. The values of S(T) in our experiments correspond to an A _d level at 0.262 eV, which is identified as the Fermi level of CuAlO₂. Based on our experimental Seebeck coefficient and the electrical conductivity, the constant relaxation time is estimated to be 1 × 10^?16 s. The power factor is large for a low A _d level and increases with temperature. It is suggested that delafossite CuAlO₂ can be considered as a promising thermoelectric oxide material at high doping and high temperature.     

Super-Large Domain Metal-Induced Radially Crystallized Poly-Si Made Using Ni(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>/NH<Subscript>4</Subscript>OH Mixed Solution

By using an aqueous solution of Ni(NO₃)₂/NH₄OH for formation of Ni media on a-Si, disk-like super-large domain metal-induced radially crystallized (S-MIRC) poly-Si was prepared. The process requires no buffer layer deposition on a-Si. The prepared S-MIRC poly-Si has an average domain size of up to 60 μm, highest hole Hall mobility of 27.1 cm² V⁻¹ s⁻¹, and highest electron Hall mobility of 45.6 cm² V⁻¹ s⁻¹. Poly-Si TFT made on super-large-domain S-MIRC poly-Si had high mobility of ~105.8 cm² V⁻¹ s⁻¹, steep sub-threshold slope of ~1.0 V decade⁻¹, high on/off state current ratio of >10⁷ and low threshold voltage of ~ −6.9 V. A simultaneous Ni-collected and induced crystallization model is proposed to explain the growth kinetics of S-MIRC poly-Si.     

Conductivity of Hg<Subscript>3</Subscript>In<Subscript>2</Subscript>Te<Subscript>6</Subscript> crystals in high electric fields

The effect of electric field and temperature on the conductivity of bulk Hg₃In₂Te₆ crystals is investigated. It is shown that the I–V characteristics in high electric fields are of the S type with the effect of switching into a low-resistance state. The critical voltage of transition from the Ohm law to the exponential dependence of the current (I) on the voltage (U) and the threshold voltage of transition into the region of negative differential resistance dU/dI = s< 0 linearly depend on the sample thickness. The activation energies of conductivity in low and high electric fields are determined. It is established that the superlinear portion of the I–V characteristic with dU/dI > 0 is described by the dependence of the type I = I ₀ exp(U/U ₀) and caused by the electron transitions from the local centers with the energy level E _t = 0.19 eV.     

Cu<Subscript>3</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>: An Ultralow-Firing Microwave Dielectric Ceramic with Good Temperature Stability and Chemical Compatibility with Aluminum

An ultralow-firing microwave dielectric ceramic Cu₃Mo₂O₉ with orthorhombic structure has been fabricated via a solid-state reaction method. X-ray diffraction analysis, Rietveld refinement, Raman spectroscopy, energy-dispersive spectrometry, and scanning electron microscopy were employed to explore the phase purity, crystal structure, and microstructure. Pure and dense Cu₃Mo₂O₉ ceramics could be obtained in the sintering temperature range from 580°C to 680°C. The sample sintered at 660°C for 4 h exhibited the highest relative density (～ 97.2%) and best microwave dielectric properties with ε _r = 7.2, Q × f = 19,300 GHz, and τ _f = ? 7.8 ppm/°C. Chemical compatibility with aluminum electrodes was also confirmed. All the results suggest that Cu₃Mo₂O₉ ceramic is a promising candidate for use in ultralow-temperature cofired ceramic applications.