Fabrication and characterization of MOCVD (In1-xAlx)2O3 (0.1≤x≤0.6) ternary films

A series of (In_1-xAl_x)₂O₃ (0.1 ≤ x ≤ 0.6) films with tunable bandgap were grown on MgO (100) substrates by MOCVD. The influences of chemical compositions and growth temperatures on the film properties were studied systematically. XRD analyses indicated that the film quality degraded from crystalline to amorphous structure as Al concentration (x) increased. The (In_1-xAl_x)₂O₃ films prepared at 700 °C exhibited better film crystallinity than those of the ones grown at 600 °C. The films prepared at 700 °C with x = 0.1–0.3 showed an epitaxial In₂O₃ <111> orientation with the corresponding growth relationship of In₂O₃ (111)∥MgO (100). The film with x = 0.2 exhibited the best crystallinity and the largest grain size of 25.9 nm. The Hall mobilities and resistivities of the films were influenced evidently by Al concentrations. The Hall mobility showed a monotonous decrease from 12 to 1.1 cm²V^?1s^?1 as x increased from 0.1 to 0.6. The lowest resistivity of 9.2 × 10^?3 Ω cm was acquired for the film with x = 0.2. The average transmittances in the visible region for all the films were beyond 83%. The bandgap of the (In_1-xAl_x)₂O₃ films can be regulated in the range of 3.85–4.88 eV by changing Al concentrations from 0.1 to 0.6.     

Thermoelectric properties of Mo-doped bulk In2O3 and prediction of its maximum ZT

In a search for new thermoelectric materials, indium oxide (In₂O₃) was selected as a candidate for high-temperature thermoelectric oxide materials due to its intrinsically low thermal conductivity (<2 W/mK) and ZT values around 0.05. However, low electrical conductivity is a factor limiting the thermoelectric performance of this oxide, and was addressed in this study by Mo doping. It was found that Mo is soluble in In₂O₃ but forms secondary phases at a fraction near x = 0.06 and higher. Mo was found to be unsuitable for heavy n-type doping necessary to improve the thermoelectric performance of the oxide to the desired level (ZT = 1). However, the experimental data enabled us to analyze the electrical conductivity behavior and the Seebeck coefficient of doped In₂O₃ with different carrier concentrations, predicting a theoretically achievable maximum power factor value of 1.77 × 10^?3 W/mK² at an optimum carrier concentration. This estimation predicts the highest ZT value of 0.75 at 1073 K, assuming the lattice thermal conductivity value remaining at an amorphous level.     

Evolution of TiOx-SiOx nano-composite during annealing of ultrathin titanium oxide films on Si substrate

This paper discusses the formation of the TiO_x-SiO_x nano-composite phase during annealing of ultrathin titanium oxide films (~27 nm). The amorphous titanium oxide films are deposited on silicon substrates by sputtering. These films are important for high-k dielectrics and sensing applications. Annealing of these films at 750 °C in the O₂ environment (for 15–60 min) resulted in the polycrystalline rutile phase. The films exhibit Raman peaks at 150 cm⁻¹ (B_1g), 435 cm⁻¹ (E_g), and 615 cm⁻¹ (A_1g) confirming the rutile phase. The signature TO (1078 cm⁻¹) and LO (1259 cm⁻¹) infrared active vibrational modes of Si–O–Si bond confirms the presence of silicon-oxide. The X-ray photoelectron spectra of the TiO_x films show multiple peaks corresponding to Ti metal (453.8 eV); Ti⁴⁺ state (458.3 eV (Ti 2p_3/2) and 464 eV (Ti 2p_1/2)); and Ti³⁺ state (456.4 eV (Ti 2p_3/2) and 460.8 eV (Ti 2p_1/2)). The O1s XPS spectra peaks at 530–533 eV can be attributed to Ti–O and Si–O bonds of the TiO_x-SiO_x nano-composite phase in the annealed films. The depth profiling XPS study shows that the top surface of the annealed film is mainly TiO_x and the amount of SiO_x increases with the depth.     

Enhancing high power performances of Pb(Mn1/3Nb2/3)O3–Pb(Zr,Ti)O3 ceramics by Bi(Ni1/2Ti1/2)O3 modification

High power piezoelectric ceramics 0.04Bi(Ni_1/2Ti_1/2)O₃-xPb(Mn_1/3Nb_2/3)O₃-(0.96-x)Pb(Zr_yTi_1-y)O₃ (BNT-xPMnN-PZ_yT) with various contents of PMnN from 0 to 12 mol% (keep y = 0.50) and Zr/Ti ratio gradually increasing from 48/52 to 52/48 (keep x = 0.06) were prepared by solid-state method. X-ray diffraction (XRD) results show a single phase of polycrystalline perovskite and indicate that the phase structure transforms from tetragonal phase to rhombohedral with x and y increasing. The optimal comprehensive properties of BNT-xPMnN-PZ_yT ceramic, d₃₃ (355 pC/N), k_p (0.58), ε_r (1512), tanδ (0.40%), T_c (336 °C) and Q_m (2010), are obtained at x = 0.06 and y = 0.50, which are apparently superior to typical or commercial Pb(Zr,Ti)O₃ (PZT) based power ceramics. Within the range from room temperature to 200 °C, the variation of electric-field induced strains is less than 8.3%, indicating its good temperature stability. The maximum vibration velocity of the ceramic at temperature rise of 20 °C is measured to be 0.92 m/s, which is about 2 times higher than that of commercial hard PZT ceramics, suggesting the BNT-xPMnN-PZ_yT ceramic is a competitive and potential candidate for power piezoelectric transduction and actuation applications.     

Stable anatase phase with a bandgap in visible light region by a charge compensated Ga–V (1:1) co-doping in TiO2

A series of charge compensated Ga–V co-doped TiO₂ samples (Ti_(1-x)(Ga_0.5V_0.5)_xO₂) have been synthesized by a modified sol-gel process. X-ray diffraction pattern shows that the anatase to rutile (A→R) onset temperature (T_O) shifts to a higher temperature, whereas the complete phase transformation temperature (T_C) shifts to a low-temperature region as compared to pure TiO₂, due to Ga–V incorporation. Ga–V co-doping helps in the transformation of some smaller sized Ti⁴⁺ to a relatively larger Ti³⁺. In the anatase phase, oxygen content also increases with increasing doping concentration, which along with the larger size of Ti³⁺ results in lattice expansion and thereby delays the T_O. In the rutile phase, oxygen vacancy increases with increasing doping concentration, which results in lattice contraction and accelerates phase transition. Grain growth process is hindered in the anatase phase (crystallites size reduces from ~15 nm (x = 0.00) to 8 nm (0.10)), whereas it is accelerated in the rutile phase as compared to pure TiO₂. In both phases bandgap (E_g) reduces to the visible light region (anatase: E_g = 3.16 eV (x = 0.00) to 2.19 eV (x = 0.10) and rutile: 3.08 eV (x = 0.00) to 2.18 eV (x = 0.10)) in all co-doped samples. The tail of the absorption edge reveals lattice distortion and increase of Urbach energy proofs the same due to co-doping. All these changes (grain growth, phase transition, and optical properties) are due to lattice distortion created by the combined effect of substitution, interstitials, and oxygen vacancies due to Ga–V incorporation in TiO₂.     

High electric field-induced strain properties in La-doped Pb(In1/2Nb1/2)O3–PbZrO3–PbTiO3 relaxor ferroelectric ceramics

Piezoelectric ceramics with high strain response and low hysteresis are highly in demand for high-performance actuator applications. Unfortunately, the trade-off relationship between large field-induced strain and low hysteresis in piezoelectric ceramics is a key challenge for designing high-performance piezoelectric actuators. Herein, ymol%La-doped 0.10 Pb(In_1/2Nb_1/2)O₃-xPbZrO₃-(0.90–x)PbTiO₃ [0.10PIN-xPZ-(0.90-x)PT: ymol%La] ternary relaxor ferroelectric ceramics were prepared by conventional solid-state reaction technique. Pb(In_1/2Nb_1/2)O₃ (PIN) as a relaxor end member was introduced into (Pb,La) (Zr,Ti)O₃ (PLZT) system to improve relaxor characteristics and strain properties. A giant strain of 0.23% was obtained in 0.10PIN-0.59PZ-0.31 PT: 8mol%La ceramic at the electric field of 20 kV/cm, with a high piezoelectric d₃₃* of 1150 pm/V and low hysteresis H_y of 6.4%, exhibiting a potential application in high-performance piezoelectric actuators. Furthermore, the effects of La ion doping and components on the ferroelectric, dielectric and electric field-induced strain properties were investigated, and provides a new way for improve the strain properties of piezoelectric materials.     

Optical transmittance and energy storage properties of potassium sodium niobate glass-ceramics

In this work, 0.8(K₂O-Na₂O-2Nb₂O₅)?0.2((1-x)B₂O₃-xP₂O₅) (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) glass-ceramics have been fabricated. The effects of P₂O₅ on the microstructure and properties of the glass-ceramics were comprehensively studied. The addition of P₂O₅ promotes the transition of the glass network structure from a negatively charged [B?₄]^- tetrahedron to an electrically neutral [BP?₄] tetrahedron. With the increase of P₂O₅ content, the formation of K₂B₄O₇ is inhibited, with major phase of Na_0.9K_0.1NbO₃ and minor phase of K₂B₄O₇. It is found that the band gap width of the glass-ceramics increases from 3.34 eV to 3.52 eV firstly and then decreases to 3.43 eV. The grain size of the glass-ceramics decreases from 150 nm to 50 nm. High optical transmittance (63%), large discharge energy density (4.58 J/cm³) and large energy storage efficiency (98%) have been simultaneously obtained for K₂O-Na₂O-Nb₂O₅-B₂O₃-P₂O₅ glass-ceramics, which are potential for the applications of the transparent pulse capacitors.     

Valence state of europium and samarium in Ln2Hf2O7 (Ln = Eu,Sm) based oxygen ion conductors

Ln₂(Hf_2-xLn_x)O_7-x/2 (Ln = Sm, Eu; x = 0.1) pyrochlores have been prepared via mechanical activation of oxide mixtures, followed by heat treatment for 4h at 1450 and 1600 °C, respectively. According to the ESR data, the Eu cations on the Hf site in the Hf_1-xEu_xO₆ octahedra in pyrochlore Eu₂(Hf_2-xEu_x)O_7-x/2 (x = 0.1) are most readily oxidized and reduced. Oxidation at 840 °C for 24h in air reduces the total conductivity of the Ln₂(Hf_2-xLn_x)O_7-x/2 (Ln = Sm, Eu; x = 0.1) by a factor of 2.5–6, due to the decrease in the concentrations of oxygen vacancies and Ln²⁺ ions as a result of the oxidation. The anomalous low-frequency behavior of the permittivity of the Eu₂(Hf_2-xEu_x)O_7-x/2 (x = 0.1) at ~800 °C can be understood in terms of the changes in the oxygen sublattice of the pyrochlore structure as a result of the oxidation of divalent europium and partial filling of oxygen vacancies at this temperature.     

Optimization,structural, optical and magnetic properties of TiO2/CoFe2O4 nanocomposites

Magneto-optical TiO₂/xCoFe₂O₄ nanocomposites having various concentrations of CoFe₂O₄ (x = 2, 4 and 6 wt %) were prepared using facile mechanical mixing. X-ray diffraction was employed for the phase examination and microstructure parameters. X-ray diffraction spectra proved the formation of two separate phases: tetragonal titanium dioxide (TiO₂) and face-centered cubic cobalt iron oxide. The structure was further verified by recognizing the selected area electron diffraction (SAED) pattern recorded by a high-resolution transmission microscope. The optical investigation of the prepared nanocomposites verified that the optical band gap values varied from 3.1 eV for pure TiO₂ to 3.05 eV for TiO₂/CoFe₂O₄ (6 wt %). The refractive index, optical dielectric constant and loss factor were discussed in detail. The nanocomposites (TiO₂/xCoFe₂O₄) demonstrated ferromagnetic characteristics and their magnetic parameters were affected by the CoFe₂O₄ percentage in the composites. The sample x = 2 wt % depicted the maximum magnetic exchange bias at room temperature. Moreover, it showed maximum coercivity (H_C) and magnetic squareness ratio (SQ), which makes it suitable for spintronic applications.     

Structural,optical and methanol sensing properties of sprayed In2O3 nanoparticle thin films

Indium oxide (In₂O₃) nanoparticle thin films were grown on cleaned glass substrates by the chemical spray pyrolysis technique using the precursor solution of indium nitrate (In (NO₃)₃). The XRD studies confirm that the films are polycrystalline In₂O₃, possessing cubic structure with lattice parameters, a = b = c = 10.17 Å. The optical studies show a direct optical band gap of 3.32 eV and an indirect band gap of 2.6 eV in the prepared films. The films exhibit high optical transparency >80% in the visible region, reaching a maximum of 85% at 684 nm wavelength. Further, the gas sensing properties of the films have been investigated for various concentrations of methanol in air at different operating temperatures. At 300 °C the film exhibits a very high response 99% to methanol vapor at a concentration of 40 ppm in air, which is ideal to be used as a methanol sensor. The film shows fast response and recovery to methanol vapor at higher operating temperatures. A possible methanol sensing mechanism has been proposed.     

Fe3+-substituted aluminium oxide nano-flakes: Structural,morphological, optical,and gas sensing properties

Mixed metal oxides with chemical formula Fe_xAl_2-xO₃ (where x = 0.2–1.0) (FANF) was synthesized via sol-gel auto combustion process. X-ray diffraction, field emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy were employed to characterize produced oxide materials. The final product FANF was sintered for 5 h at 1100 °C. The TG-DTA validated the mixed metal oxides phase evolution and steady-state temperature. The replacement of aluminium ions results in orthorhombohedral structure in mixed metal oxides (MMO). The bandgap decreased from 3.72 eV to 3.21 eV and the crystallite size decreased from 28 nm to 14 nm as the iron content increased in the sample Fe_xAl_2-xO₃ (where x = 0.2–1.0). The FT-IR confirmed no impurity peaks and the single phase with iron oxide band is near 432 cm^?1, while the aluminium oxide band is 565–600 cm^?1. Microstructural investigation shows flake-like growth, and EDS confirmed a stoichiometric ratio of MMO. Iron-substituted aluminate gas sensors detected CO, H₂S, and NO₂ at temperature ranging from 25 to 300 °C. Fe_0.6Al_1.4O₄ (F₃ANF) sensor responded 46.69% towards 100 ppm H₂S at 200 °C. Overall, the results showed that a flake-like FANF sensor can be used effectively as a H₂S gas sensor.     

Role of Ni2+ substituent on the structural,optical and magnetic properties of chromium oxide (Cr2-xNixO3) nanoparticles

Pristine chromium oxide (Cr₂O₃) and nickel ions (Ni²⁺) substituted Cr₂O₃ nanoparticles were synthesized using a simple co-precipitation technique. The main objective of this work is to investigate Ni²⁺ substituent's role at different concentrations on the structural, morphological, optical, and magnetic properties of Cr₂O₃ nanoparticles. Structural analyses based on X-ray diffraction (XRD), Raman and Fourier transform infra-red (FTIR) data confirmed the successful incorporation of Ni²⁺ into Cr₂O₃ nanoparticles up to x = 0.05 of Ni²⁺ content, without affecting the rhombohedral crystal structure of Cr₂O₃ nanoparticles. Rietveld refinement results showed the variation in lattice parameters and cell volumes alongwith the substitution of Ni²⁺ into Cr₂O₃ nanoparticles. Raman and FTIR spectra also depicted a considerable shift in the characteristic vibration modes of Cr₂O₃ nanoparticles due to strain-induced by Ni²⁺ substitution. Beyond x = 0.05, the structural transformation took place from rhombohedral to cubic crystal structure. Subsequently, new peaks (apart from Cr₂O₃ phase modes) have been observed at x = 0.1 of Ni²⁺ content due to the formation of secondary phase i.e., nickel chromate (NiCr₂O₄). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) illustrated the changes in the morphology of Cr₂O₃ nanoparticles with Ni²⁺ substitution. UV–Vis analysis revealed a narrowing of optical band energy (E_g) of Ni²⁺ substituted Cr₂O₃ nanoparticles from 3 to 1.85 eV as Ni²⁺ content varies from x = 0 to 0.2, respectively. Afterward, there is an increase in optical band gap energy (E_g) when Ni²⁺ content increased from x = 0.3 to 0.5, as NiCr₂O₄ started dominating the Cr₂O₃ phase. Single-phase Ni²⁺ substituted Cr₂O₃ nanoparticles exhibited a superparamagnetic behavior, whereas the multi-phase compound ascribed to both superparamagnetic and paramagnetic. These changes in optical and magnetic properties can lead to novel strategies to render applications in the field of optoelectronics and optomagnetic devices.     

Ablation behavior of (Hf–Ta–Zr–Nb–Ti)C high-entropy carbide and (Hf–Ta–Zr–Nb–Ti)C–xSiC composites

The ablation behavior of (Hf–Ta–Zr–Nb–Ti)C high-entropy carbide (HEC-0) was investigated using a plasma flame in air for different times (60, 90, and 120 s) at about 2100°C. The effect of SiC content on the ablation resistance of HEC–xSiC composites (x = 10 and 20 vol%) was also studied. The linear ablation rate of HEC-0 decreases with increasing ablation time, showing the positive role of the oxide layer with a complex composition. The linear ablation rate of HEC–10 vol% SiC (0.3 µm s⁻¹) is only a 10th of that of HEC-0, showing a significant improvement in ablation resistance, probably due to the formation of a protective oxide layer containing melted SiO₂ and refractory Hf–Zr–Si–O oxides.     

Lead zirconium titanate thin films prepared by thermal annealing of multilayer structures composed of PbO,ZrO2 and TiO2

Lead zirconium titanate [Pb(Zr_xTi_1?x)O₃ or PZT] thin films were prepared by the thermal annealing of multilayer films composed of binary oxide layers of PbO, ZrO₂ and TiO₂. The binary oxides were deposited by metal organic chemical vapor deposition. An interdiffusion reaction for perovskite PZT thin films was initiated at approximately 550 °C and nearly completed at 750 °C for 1 h under O₂ annealing atmosphere. The composition of Pb/Zr/Ti in perovskite PZT could be controlled by the thickness ratio of PbO/ZrO₂/TiO₂ where the contribution of each binary oxide at the same thickness was 1:0.55:0.94. The electrical properties of PZT (Zr/Ti = 40/60, 300 nm) prepared on a Pt-coated substrate included a dielectric constant ?_r of 475, a coercive field E_c of 320 kV/cm, and remnant polarization P_r of 11 μC/cm² at an applied voltage of 18 V.     

Effect of site occupancies of rare earth ions on electrical properties in Ni-MLCC based on BaTiO3

The site occupancies of rare earth ions for Ba-site to Ti-site were quantitatively estimated in (Ba_1−x,R_x)(Ti_1−x,R_x)O₃ (R = Eu, Ho), (Ba_1−3xEu_2x)TiO₃, and Ba(Ti_1−2xEu_2x)O_3−x systems by applying the Rietveld refinement to the data obtained from the synchrotron radiation powder diffraction measurement. The occupational ratio of Ba-site to Ti-site for the larger rare earth ion (Eu) was 49/51 (x = 0.10), whereas for the smaller ion (Ho) was 9/91 (x = 0.01) in (Ba_1−x,R_x)(Ti_1−x,R_x)O₃ system. Furthermore, the occupational ratio was greatly dependent on the Ba/Ti ratio, in (Ba_1−3xEu_2x)TiO₃ system it was 92/8 (x = 0.03), whereas that in Ba(Ti_1−2xEu_2x)O_3−x system was 20/80 (x = 0.01). The Curie point shifted to lower temperature effectively with increasing in the occupational ratio of rare earth ion into Ba-site.     

Effect of isovalent substitution on phase transition and negative thermal expansion of In2−xScxW3O12 ceramics

Solid solutions of In_2−xSc_xW₃O₁₂ (0≤x≤2) were successfully synthesized using the solid state reaction method. Effects of substituted scandium content on the phase composition, microstructure, phase transition temperatures and thermal expansion behaviors of the resulting In_2−xSc_xW₃O₁₂ (0≤x≤2) samples were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and thermal mechanical analyzer (TMA). Results indicate that the obtained In₂W₃O₁₂ ceramic undergoes a structure phase transition from monoclinic to orthorhombic at 248 °C. This phase transition temperature of In₂W₃O₁₂ can be easily shifted to a lower temperature by partly substituting the In³⁺ with Sc³⁺. When the x value increased from 0 to 1, the phase transition temperatures of In_2−xSc_xW₃O₁₂ (0≤x≤2) samples decreased from 248 to 47 °C. All the In_2−xSc_xW₃O₁₂ (0≤x≤2) ceramics show fine negative thermal expansion below their corresponding phase transition temperatures. The negative thermal expansion coefficients of the In_2−xSc_xW₃O₁₂ (0≤x≤2) ceramics change in the range from −1.08×10⁻⁶ °C⁻¹ to −7.13×10⁻⁶ °C⁻¹.     

Optimized phase compositions and microwave dielectric properties of low loss Ca2Sn2Al2O9-based ceramics by M4+ substitution

The traditional solid-state reaction method was used to prepare Ca₂Sn_2−xM_xAl₂O₉ (M = Ti, Zr, and Hf) ceramics. Then, the impact of an M⁴⁺ substitution of Sn⁴⁺ on the phase transition, crystal structural parameter, and microwave dielectric properties of Ca₂Sn_2−xM_xAl₂O₉ (0 ≤ x ≤ 0.4) ceramics were investigated. Ti⁴⁺ could not replace the Sn⁴⁺ of Ca₂Sn₂Al₂O₉ due to its small ionic radius, and the Al-based second phases of Ca₂Sn_2−xTi_xAl₂O₉ ceramics were confirmed by the X-ray diffractometer and EDS map scanning results. With the Zr⁴⁺ and Hf⁴⁺ substitutions of Sn⁴⁺, the SnO₂ and CaSnO₃ second phases of Ca₂Sn₂Al₂O₉ ceramic were inhibited, and the Ca₂Sn_2−xM_xAl₂O₉ (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) single-phase ceramics with orthorhombic structure (Pbcn space group) were obtained. New MO₂ (M = Zr and Hf) and CaAl₂O₄ second phases appeared in the Ca₂Sn_2−xM_xAl₂O₉ (M = Zr and Hf) (0.3 ≤ x ≤ 0.4) ceramics, and their contents increased gradually with the increase in x. The Ca₂Sn_2−xM_xAl₂O₉ (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) ceramics exhibited high Q × f because of their pure phase compositions, and the Q × f of Ca₂Sn₂Al₂O₉ ceramic was improved to 77 800 GHz (12.6 GHz) in the Ca₂Sn_1.9Zr_0.1Al₂O₉ ceramic. The Q × f values of Ca₂Sn_2−xM_xAl₂O₉ single-phase ceramics were mainly controlled by r_c (Sn/M–O) and r_c (Al–O). The τ_f values of single-phase Ca₂Sn_2−xM_xAl₂O₉ ceramics were related to octahedral distortions. The Zr⁴⁺ and Hf⁴⁺ substitution of Sn⁴⁺ optimized the phase compositions and microwave dielectric properties of the Ca₂Sn_2−xM_xAl₂O₉ ceramics, and the Ca₂Sn_1.9Zr_0.1Al₂O₉ ceramic sintered at optimal temperature exhibited excellent microwave dielectric properties (ε_r = 8.67, Q × f = 77 800 GHz at 12.6 GHz and τ_f = −69.8 ppm/°C).     

Crystal structure,far-infrared spectra,and microwave dielectric properties of bazirite-type BaZr(Si1-xGex)3O9 ceramics

Novel BaZr(Si_1-xGe_x)₃O₉ (0 ≤ x ≤ 1.0) microwave dielectric ceramics were prepared by solid-state reaction sintering at 1200–1450 °C for 5 h Ge⁴⁺ ions occupied the Si⁴⁺ positions, and BaZr(Si_1-xGe_x)₃O₉ solid solutions were obtained. The BaZr(Si_1-xGe_x)₃O₉ (0 ≤ x ≤ 1.0) ceramics exhibited hexagonal structures with P-6c2 space groups and octahedral layers and [Si/Ge₃O₉]^6- rings. Owing to these structural characteristics, the ceramics exhibited low permittivity. With an increase in x, the relative permittivity (ε_r) values of the BaZr(Si_1-xGe_x)₃O₉ (0 ≤ x ≤ 1.0) ceramics increased from 7.68 (x = 0) to 9.45 (x = 1.0), while their quality factor (Q × f) values first increased and then decreased. The Q × f value (10,300 GHz at 13.43 GHz) of the BaZrSi₃O₉ (x = 0) ceramic improved with the substitution of Si⁴⁺ by Ge⁴⁺. A high Q × f value (36,100 GHz at 13.81 GHz) was obtained for the BaZr(Si_1-xGe_x)₃O₉ (x = 0.2) ceramic, and the Q × f values of the BaZr(Si_1-xGe_x)₃O₉ ceramics could be controlled by varying the Si/Ge-site bond valence. The temperature coefficient of resonance frequency (τ_f) values of the BaZr(Si_1-xGe_x)₃O₉ ceramics were mainly affected by the O2-site bond valence, and the optimum τ_f value (?22.8 ppm/°C) was achieved for the BaZrSi₃O₉ ceramic. The BaZr(Si_1-xGe_x)₃O₉ (x = 0.2) ceramic showed the optimum microwave dielectric properties (ε_r = 8.36, Q × f = 36,100 GHz at 13.81 GHz, and τ_f = ?34.5 ppm/°C).     

The structure and properties of 0.95MgTiO3–0.05CaTiO3 ceramics co-doped with ZnO–ZrO2

The (Mg_0.93Ca_0.05Zn_0.02)(Ti_1?xZr_x)O₃ ceramics were prepared by conventional solid-state route. The dielectric properties and structure of (Mg_0.93Ca_0.05Zn_0.02)(Ti_1?xZr_x)O₃ ceramics were investigated. It has been found that MgTiO₃ and CaTiO₃ are the main phases and a second phase CaZrTi₂O₇ appeared in 95MCT ceramics co-doped with Zn–Zr. With Zn–Zr additive, the sintering temperature of 95MCT ceramics can be reduced to 1300 °C, and adjust the temperature coefficient of dielectric constant. With the increasing of Zr content, dielectric constant ?_r decrease from 22.6 to 19.91 and the temperature coefficient of dielectric constant α_c from 5.93 to 2.52 ppm/°C when x = 0.01, 0.02, 0.03 and 0.04 mol respectively. The 95MCT ceramics with x = 0.02 has a dielectric constant ?_r of 22.02, a dielectric loss of 2.78 × 10^?4 and a temperature coefficient of dielectric constant α_c value of 2.98 ppm/°C.     

Effect of nonstoichiometry on the structure and microwave dielectric properties of Ba(Co1/3Nb2/3)O3 ceramics

The effect of B-site cation deficiency on the structure and microwave dielectric properties of Ba(Co_1/3Nb_2/3)O₃ (BCN) was investigated. Stoichiometric and co-deficient compositions based on Ba(Co_1/3−xNb_2/3)O₃ [x = 0.0, 0.01, 0.02, 0.03 and 0.04] were prepared using the conventional mixed oxide route. Small amounts of V₂O₅ (0.1 wt%) were added to promote densification. The dielectric loss is very sensitive to the composition; it was found that co-deficiency degraded the microwave dielectric properties. The stoichiometric formulation (x = 0) exhibited the best microwave properties. The improvements in the microwave dielectric properties were achieved by increasing the degree of 1:2 cation ordering. The highly ordered, stoichiometric BCN ceramics showed a relative permittivity (ɛ_r) of 32, quality factor (Q × f) of 66,500 GHz and a negative temperature coefficient of resonant frequency (τ_f) of −10 ppm/°C at 4 GHz.