Signature of lattice defects in far infrared reflectivity of Ba(Mg1/3Ta2/3)O3

Far infrared reflectivity spectra of Ba(Mg_1/3,Ta_2/3)O₃ prepared at several sintering temperatures were measured, and the eigenfrequencies and damping constants of the TO modes were determined. The reflectivity spectra were fitted with the four-parameter semi-quantum model. The variation in the E_u(O_II) at 222 cm⁻¹ and A_2u(O_II) at 238 cm⁻¹ modes in well ordered ceramics was attributed to the variation in the concentration of the B site defects. It was also found that the change in the oxygen partial pressure of the sintering atmosphere causes a change in the seventh (316 cm⁻¹) and eighth (352 cm⁻¹) modes. We attribute these changes to the oxygen site defect although we cannot evaluate the concentration of this defect at this moment. From the behavior of the damping constants it is suggested that the Ba(Mg_1/3Ta_2/3)O₃ (BMT) attains equilibrium defect density at the heat treatment temperature of more than 1630 °C (120 h).     

Investigation of Raman Modes and Born‐Effective Charges in AgNb1/2Ta1/2O3: A Density‐Functional and Raman Scattering Study

Using ab initio density‐functional theory, the Born‐effective charge tensors and zone‐center phonon mode frequencies are computed for AgNb_1/2Ta_1/2O₃ in monoclinic P2/m and orthorombic Pbcm symmetries. The experimental mode frequencies are obtained from deconvolution of Raman spectrum of prepared AgNb_1/2Ta_1/2O₃ samples and are compared with computed mode frequencies. The Raman modes with high (>350 cm^?1) and low frequencies (<90 cm^?1) correspond to Ag and O vibrations, respectively. The modes in intermediate frequency band (120–350 cm^?1) are dominated by Nb(Ta)–O vibrations. The computed effective charge tensors of cations at A (Ag) and B (Nb, Ta) sites are found to be diagonal. The off‐diagonal components of charge tensor are found sizeable only for O ions in orthorhombic AgNb_1/2Ta_1/2O₃ with Pbcm symmetry. Further, charge tensor structure of O ions is found to depend on site symmetry in the unit cell. Charge tensor components for Nb, Ta, and O ions differ significantly from their nominal ionic values suggesting (1) large local dipole moments induced by off‐centering of Nb(Ta) ions and tilting(rotations) of Nb(Ta)O₆ octahedra, (2) hybridization between d‐orbitals of Nb(Ta) and p‐orbitals of O atoms. Furthermore, the electronic structure, directional dependence of effective charges and performance of LDA (GGA) exchange‐correlation functionals with regard to computed values are also discussed.     

Lattice dynamics of yttria: A combined investigation from spectrum measurements and first-principle calculations

C-type Y₂O₃ ceramics (relative density ~94%) were prepared at 1500 °C for 2 hours with 1% wt. ZnO as sintering aid. The cell parameters of Y₂O₃ from Rietveld refinements are a = 10.6113(1) Å, V = 1194.8(1) ų. The vibrational modes / lattice dynamics of Y₂O₃ were investigated using vibrational spectra (Raman and infrared reflection spectra) and first-principle (DFT) calculations. Eight of the 22 predicted first-order Raman modes and 12 of 16 predicted IR modes are observed and reliably assigned. For the observed vibrational modes, an excellent linearity (f_exp = 1.023f_theo, R² = 0.9999) between frequency from calculations (f_theo) and that from measurements (f_exp) is observed. Accordingly, the corrected frequency (f_cor) of vibrational modes, phonon band structure, and density of phonon states (DOPS) of Y₂O₃ are presented, in which, the frequency of phonons of Y₂O₃ is ≤625.2 cm⁻¹ (wavelength ≥16.0 μm) with a gap of 30.6 cm⁻¹ from 486.0 to 516.6 cm⁻¹ (wavelength 20.6 - 19.4 μm) at room temperature. The modes with f_theo ≥292.5 cm⁻¹ (f_cor ≥299.2 cm⁻¹) are dominated by the vibrations of O²⁻ (light atom vibrations) and the vibrational modes with f_theo ≤239.0 cm⁻¹ (f_cor ≤244.5 cm⁻¹) are dominated by the vibrations of both Y³⁺ and O²⁻ (co-vibrations). The three modes T_u⁽⁷⁾ at 301.6 cm⁻¹, T_u⁽¹⁰⁾ at 333.7 cm⁻¹, and T_u⁽¹²⁾ at 369.7 cm⁻¹ of Y-O stretch vibrations dominate the phonon dielectric constant and dielectric loss of Y₂O₃ with more than 85% contributions.     

Achieving single domain in rhombohedral and tetragonal Mn-doped Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 crystals for infrared detecting applications

The [111]-oriented rhombohedral Mn-doped 0.15Pb(In_1/2Nb_1/2)-0.55Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (Mn:PIMNT(15/55/30)) crystal and the [001]-oriented tetragonal Mn-doped 0.29Pb(In_1/2Nb_1/2)-0.29Pb(Mg_1/3Nb_2/3)O₃-0.42PbTiO₃ (Mn:PIMNT(29/29/42)) crystal were poled under different conditions. The pyroelectric performance of the two crystals as a function of poling temperature, as well as the relationship with ferroelectric domain configuration and phase structure was investigated systematically. The pyroelectric properties of the two crystals enhance with rising the poling temperature, which can be attributed to the improvement of the single state. And for the rhombohedral Mn:PIMNT(15/55/30) crystal locating near morphotropic phase boundary (MPB), the increase of tetragonal phase induces the deterioration of pyroelectric properties. Due to more residual tetragonal phase, the pyroelectric coefficient of the Mn:PIMNT(15/55/30) crystal poled at 150°C is lower than that poled at 100°C. In general, both the crystals poled above T_C achieve nearly single state, exhibiting the best pyroelectric properties with relatively high Curie temperature (T_C), where P = 9.71 × 10⁻⁴ C m⁻² K⁻¹, F_i = 3.88 × 10⁻¹⁰ m V⁻¹, F_v = 0.068 m² C⁻¹ and F_d = 29.7 × 10⁻⁵ Pa^−1/2 for the rhombohedral Mn:PIMNT(15/55/30) crystal (T_C = 171°C) and P = 6.78 × 10⁻⁴ C m⁻² K⁻¹, F_i = 2.71 ×10⁻¹⁰ mV⁻¹, F_v = 0.1 m² C⁻¹, F_d = 23.54 × 10⁻⁵ Pa^−1/2 for the tetragonal Mn:PIMNT(29/29/42) single crystal (T_C = 251°C), meeting the stable operation of infrared detector at relatively high environmental temperatures.     

Photoluminescence and electrochemical performance evaluation of Eu3+ doped MgAl2O4 phosphors for LED and energy storage applications

Crystal structure of Eu³⁺ doped MgAl₂O₄ (MAO) phosphors synthesised by solid state reaction method was investigated using X-ray diffraction. Raman peaks appeared at 307 cm^?1, 408 cm^?1, 668 cm^?1 and 767 cm^?1 were assigned to F_2g (1), F_2g (2), E_g and A_1g respectively. Spherical morphology and microstructural analysis of synthesised phosphors was analysed by Field emission scanning electron microscope (FESEM) high resolution transmission electron microscope (HRTEM) and energy dispersive X-ray analysis (EDAX) was used to establish the chemical composition of the phosphors. Optical properties were analysed by photoexcitation (394 nm) and photoluminescence (PL) spectra displayed all the characteristic emission of Eu³⁺ related to transition ⁵D₀ to ⁷F_j (j = 0, 1, 2, 3, 4). The emission color was observed in red region and it was confirmed by the Commission Internationale de l’Eclairage (CIE) chromatic coordinate graph. The color purity and quality (correlated color temperature- CCT value) of red light was observed in 0.9% Eu³⁺ doped MAO to be 90.76% and 2097K respectively. Electrochemical evaluation of Eu³⁺ doped MAO was performed through cyclic voltammetry (CV) studies.     

Enhanced pyroelectric properties in (Bi0.5Na0.5)TiO3–BiAlO3–NaNbO3 ternary system lead‐free ceramics

High pyroelectric performance and good thermal stability of pyroelectric materials are desirable for the application of infrared thermal detectors. In this work, enhanced pyroelectric properties were achieved in a new ternary (1?x)(0.98(Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃–0.02BiAlO₃)–xNaNbO₃ (BNT–BA–xNN) lead‐free ceramics. The effect of NN addition on the microstructure, phase transition, ferroelectric, and pyroelectric properties of BNT–BA–xNN ceramics were investigated. It was found that the average grain size decreased as x increased to 0.03, whereas increased with further NN addition. The pyroelectric coefficient p at room temperature (RT) was significantly increased from 3.87 × 10^?8Ccm^?2K^?1 at x = 0 to 8.45 × 10^?8Ccm^?2K^?1 at x = 0.03. The figures of merit (FOMs), F_i, F_v and F_d, were also enhanced with addition of NN. Because of high p (7.48 × 10^?8Ccm^?2K^?1) as well as relatively low dielectric permittivity (~370) and low dielectric loss (~0.011), the optimal FOMs at RT were obtained at x = 0.02 with F_i = 2.66 × 10^?10 m/V, F_v = 8.07 × 10^?2 m²/C, and F_d = 4.22 × 10^?5 Pa^?1/2, which are superior to other reported lead‐free ceramics. Furthermore, the compositions with x ≤ 0.03 exhibited excellent temperature stability in a wide temperature range from 20 to 80°C because of high depolarization temperature (≥110°C). Those results unveil the potential of BNT–BA–xNN ceramics for infrared detector applications.     

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.     

New Antiferroelectric Solid Solution of Pb(Mg1/2W1/2)O3–Pb(Zn1/2W1/2)O3 as Dielectric Ceramics

A new solid solution of (1?x)Pb(Mg_1/2W_1/2)O₃–xPb(Zn_1/2W_1/2)O₃ has been prepared in the form of ceramics by solid‐state reaction with composition x up to 30%. It is found that with the substitution of Zn²⁺ for Mg²⁺ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T_C of PMW increases from 40°C (x = 0) to 67°C (x = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X‐ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group (Pmcn) with a decrease in lattice parameter a, but an increase in b and c as the Zn²⁺ concentration increases. The low dielectric constant (~ 10²), low dielectric loss (tanδ ≈ 10^?3), linear‐field‐induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.     

Structure and microwave dielectric properties of 1:1 ordered Nd[(Mg1-xZnx)1/2Ti1/2]O3 complex perovskite ceramics

Nd[(Mg_1-xZn_x)_1/2Ti_1/2]O₃ perovskite ceramics (x = 0, 0.2, 0.4, 0.6, 0.8) are prepared by the solid-state reaction method. The effects of Zn²⁺ substitution on the structure, microstructure, especially the B-site 1:1 cation ordering and microwave dielectric properties have been investigated. Sintered Nd[(Mg_1-xZn_x)_1/2Ti_1/2]O₃ ceramics all adopt dense microstructure, along with increased dimensional uniformity as Zn²⁺ substitution. All the ceramics are confirmed to have B-site 1:1 ordered monoclinic perovskite structure with P2₁/n space group. Atomic mass difference of B-site elements might be an important factor affecting the B-site 1:1 cation ordering. HRSTEM observation suggest that the doped Zn²⁺ cations have roughly entered the Mg²⁺ sites to promote 1:1 cation ordering. The degree of the 1:1 cation ordering can be negatively reflected by the full width at half maximum (FWHM) of F_2g(B) mode at 372 cm^?1 in Raman spectra. With Zn²⁺ doping, the degree of the 1:1 cation ordering first increases then decreases, and reaches its maximum at x = 0.6. Meanwhile the best combination of microwave dielectric properties is obtained, as ε_r = 31.4, Q × f = 74,000 GHz, τ_f = ?44 ppm/°C. It is found that the long-range ordering not only decreases the dielectric loss but also affects the dielectric constant, providing a theoretical foundation to understand further the correlation between ionic configuration and microwave dielectric properties.     

Mixed alkaline‐earth effect on the mechanical and rheological properties of Ca–Mg silicate glasses

In this article, we investigate the mixed alkaline‐earth effect in a silicate glass series with varying the molar ratio of [MgO]/([CaO]+[MgO]). This effect manifests itself as a minimum in Vickers microhardness (H_V), coefficient of thermal expansion (CTE), and isokom temperatures at 10¹²(T_g) and 10² Pa·s, and as a maximum in liquid fragility. To probe the structural origin of the mixed alkaline‐earth effect in CTE and H_v, we conducted the Raman measurements. In contrast to the aluminosilicate glasses, the present glass series exhibit a negative deviation of shift of peak position at ~1100 cm^?1 from a linear additivity, indicating the role of the aluminum speciation in affecting the vibration modes. By fitting the Vogel–Fulcher–Tamann equation to the high‐temperature viscosity data, we found a near‐linear increase of the fractional free volume with the gradual substitution of Ca by Mg, confirming the dynamic structural mismatch model describing the mixed modifier effect. This work gives insight into the mixed modifier effect in glassy systems.     

Electrochemical behavior of CuO/rGO nanopellets for flexible supercapacitor,non-enzymatic glucose,and H2O2 sensing application

In the present article, graphene oxide (GO) sheets and monoclinic copper oxide (CuO) nanocrystals are connected with each other and result in the formation of CuO/rGO nanopellets, and these nanopellets synthesized using coprecipitation method. The nanopellet structured CuO/rGO composite on carbon cloth, which act as current collector exhibits specific capacitance of 188 F g^?1 at a current density of 0.2 A g^?1 and up to 96.3% capacity retention after 2000 charge-discharge cycles. It shows a maximum energy density of 7.32 Wh kg^?1 and power density of 53 W kg^?1. The glucose sensing characteristics of CuO/rGO nanopellet is investigated on carbon cloth and ITO substrate. It shows glucose sensitivity of 0.805 mA mM^?1 cm^?2 and 0.2982 mA mM^?1 cm^?2 for a bundle like structured CuO/rGO composite on carbon cloth and ITO substrate, respectively. Further H₂O₂ sensing is studied on ITO substrate, which manifests H₂O₂ sensitivity of 84.39 μA mM^?1 cm^?2. The results indicate that nanopellet structured CuO/rGO composite could be a promising electrode material for supercapacitor, glucose, and H₂O₂ sensor.     

Efficiency above 6% in poly(3‐hexylthiophene):phenyl‐C‐butyric acid methyl ester photovoltaics via simultaneous addition of poly(3‐hexylthiophene) based grafted graphene nanosheets and hydrophobic block copolymers

A combination of reduced graphene oxide (rGO) nanosheets grafted with regioregular poly(3‐hexylthiophene) (P3HT) (rGO‐g‐P3HT) and P3HT‐b‐polystyrene (PS) block copolymers was utilized to modify the morphology of P3HT:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) active layers in photovoltaic devices. Efficiencies greater than 6% were acquired after a mild thermal annealing. To this end, the assembling of P3HT homopolymers and P3HT‐b‐PS block copolymers onto rGO‐g‐P3HT nanosheets was investigated, showing that the copolymers were assembled from the P3HT side onto the rGO‐g‐P3HT nanosheets. Assembling of P3HT‐b‐PS block copolymers onto the rGO‐g‐P3HT nanosheets developed the net hole and electron highways for charge transport, thereby in addition to photoluminescence quenching the charge mobility (μ_h and μ_e) values increased considerably. The best charge mobilities were acquired for the P3HT₅₀₀₀₀:PC71BM:rGO‐g‐P3HT₅₀₀₀₀:P3HT₇₀₀₀‐b‐PS₁₀₀₀ system (μ_h = 1.9 × 10^?5 cm² V^–1 s^–1 and μ_e = 0.8 × 10^?4 cm² V^–1 s^–1). Thermal annealing conducted at 120 °C also further increased the hole and electron mobilities to 9.8 × 10^?4 and 2.7 × 10^?3 cm² V^–1 s^–1, respectively. The thermal annealing acted as a driving force for better assembly of the P3HT‐b‐PS copolymers onto the rGO‐g‐P3HT nanosheets. This phenomenon improved the short circuit current density, fill factor, open circuit voltage and power conversion efficiency parameters from 11.13 mA cm^?2, 0.63 V, 62% and 4.35% to 12.98 mA cm^?2, 0.69 V, 68% and 6.09%, respectively. © 2019 Society of Chemical Industry     

Enhanced Infrared Absorption of C60 on Thin Evaporated Pd Island Films

Infrared transmission spectra of C₆₀ multilayers on thin Pd films deposited onto surface-oxidized Si(100) and hydrogen-terminated Si(111) substrates are reported. In both cases, the spectra in the 1500–1100 cm⁻¹ region exhibited bands at 1444, 1429, and 1182 cm⁻¹ due, respectively, to the A_g (2), T_1u (4), and T_1u (3) modes. The appearance of the A_g (2) mode, which is originally infrared inactive (Raman active), reveals electron transfer from the metal to chemisorbed C₆₀. Indeed, increasing the thickness of C₆₀, the A_g (2) mode intensity saturated more rapidly than the T_1u (4) and T_1u (3) modes. The originally infrared active T_1u (4) and T_1u (3) modes were enhanced in intensity depending upon the Pd thickness. Actually, while both substrates gave nearly the same magnitude of enhancement, the optimum Pd thickness was smaller on the hydrogen-terminated surface than on the surface-oxidized surface. On the other hand, the A_g (2) mode was less intense on the hydrogen-terminated surface than on the oxidized surface, suggestive of a shortage of chemisorbed C₆₀ and thus pointing out the importance of the metal film morphology. Indeed, Pd films deposited on the two substrates gave rise to quite different AFM images. We also show that, regardless of the substrate, the A_g (2) mode is an order of magnitude smaller than for Ag deposition, though no remarkable intensity differences were observed with respect to the T_1u (4) and T_1u (3) modes.     

Large electrocaloric responses in [Bi1/2(Na,K)1/2]TiO3‐based ceramics with giant electro‐strains

The electrocaloric effect (ECE) is investigated through indirect measurement in two lead‐free [Bi_1/2(Na,K)_1/2]TiO₃‐based ceramics that were previously reported to display giant electro‐strains. In the Nb‐doped ceramic, denoted as BNKT‐2.5Nb, a decent temperature change of ΔT=1.85 K and an electrocaloric responsivity of ΔT/ΔE=0.37 (10^?6Km V^?1) are found around room temperature (32°C). While in the Ta‐doped ceramic, BNKT‐1.5Ta, a wide operation temperature range (T_span ~55 K) is observed near room temperature. Additional electrical measurements, as well as transmission electron microscopy experiments, are performed to identify the mechanisms of the ECE in both ceramics.     

Local Structure Evolution in Ba‐Substituted Pb(Fe1/2Nb1/2)O3 Ceramics

Evolution of crystal structure in Pb_1‐xBa_x(Fe_1/2Nb_1/2)O₃ ceramics has been investigated by X‐ray diffraction and Raman spectra analysis together with the dielectric characterization. The crystal structure for all compositions is cubic and the cell volume indicates a sudden change at x = 0.075. Pb_1‐xBa_x(Fe_1/2Nb_1/2)O₃ ceramics with x > 0.075 are paraelectric, whereas those for x < 0.075 are ferroelectric at room temperature. The evolution of phonon modes indicates that the ferroelectricity of Pb_1‐xBa_x(Fe_1/2Nb_1/2)O₃ solid solution ceramics is caused by the off‐center Nb⁵⁺ in BO₆ octahedron. The ferroelectric‐related distortion is still observed in paraelectric solid solutions with x > 0.075.     

Improved stability in P3HT:PCBM photovoltaics by incorporation of well‐designed polythiophene/graphene compositions

Morphological and photovoltaic stabilities of poly(3‐hexylthiophene) (P3HT):phenyl‐C₆₁‐butyric acid methyl ester (PC₇₁BM) solar cells were investigated in pristine and modified states. To this end, four types of patterned/assembled nanostructures, namely reduced graphene oxide (rGO)‐g‐poly(3‐dodecylthiophene)/P3HT patched‐like pattern, rGO–polythiophene/P3HT/PC₇₁BM nanofiber, rGO‐g‐P3HT/P3HT cake‐like pattern and supra(polyaniline (PANI)‐g‐rGO/P3HT), were designed on the basis of rGO and various conjugated polymers. Intermediately covered rGO nanosheets by P3HT crystals (supra(PANI‐g‐rGO/P3HT)) performed better than sparsely (patched‐like pattern) and fully (cake‐like pattern) covered ones in P3HT:PC₇₁BM solar cell systems. Supra(PANI‐g‐rGO/P3HT) nanohybrids largely phase‐separated in active layers (root mean square = 0.88 nm) and also led to the highest performance (power conversion efficiency of 5.74%). The photovoltaic characteristics demonstrated decreasing trends during air aging for all devices, but with distinct slopes. The steepest decreasing plots were obtained for the unmodified P3HT:PC₇₁BM devices (from 1.77% to 0.28%). The two supramolecules with the most ordered structures, that is, cake‐like pattern (10.12 mA cm^?2, 51%, 0.58 V, 2.2 × 10^?6 cm² V^?1 s^?1, 4.3 × 10^?5 cm² V^?1 s^?1, 0.69 nm and 2.99%) and supra(PANI‐g‐rGO/P3HT) (12.51 mA cm^?2, 57%, 0.63 V, 1.2 × 10^?5 cm² V^?1 s^?1, 3.4 × 10^?4 cm² V^?1 s^?1, 0.82 nm and 4.49%), strongly retained morphological and photovoltaic stabilities in P3HT:PC₇₁BM devices after 1 month of air aging. According to the morphological, optical, photovoltaic and electrochemical results, the supra(PANI‐g‐rGO/P3HT) nanohybrid was the best candidate for stabilizing P3HT:PC₇₁BM solar cells. © 2020 Society of Chemical Industry     

High quality factor microwave dielectric ceramics in the (Mg1/3Nb2/3)O2–ZrO2–TiO2 ternary system

Novel high quality factor microwave dielectric ceramics (1?x)ZrTiO₄?x(Mg_1/3Nb_2/3)TiO₄ (0.325≤x≤0.4) and (ZrTi)_1?y(Mg_1/3Nb_2/3)_yO₄ (0.2≤y≤0.5) with the addition of 0.5 wt% MnCO₃ in the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system were prepared, using solid‐state reaction method. The relationship between the structure and microwave dielectric properties of the ceramics was studied. The XRD patterns of the sintered samples reveal the main phase belonged to α‐PbO₂‐type structure. Raman spectroscopy and infrared reflectivity (IR) spectra were employed to evaluate phonon modes of ceramics. The 0.65ZrTiO₄?0.35(Mg_1/3Nb_2/3)TiO₄?0.5 wt% MnCO₃ ceramic can be well densified at 1240°C for 2 hours and exhibits good microwave dielectric properties with a relative permittivity (ε_r) of 42.5, a quality factor (Q×f) value of 43 520 GHz (at 5.9 Ghz) and temperature coefficient of resonant frequency (τ_f) value of ?5ppm/°C. Furthermore, the (ZrTi)_0.7(Mg_1/3Nb_2/3)_0.3O₄?0.5 wt% MnCO₃ ceramic sintered at 1260°C for 2 hours possesses a ε_r of 31.8, a Q×f value of 35 640 GHz (at 6.3 GHz) and a near zero τ_f value of ?5.9 ppm/°C. The results demonstrated that the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system with excellent properties was a promising material for microwave electronic device applications.     

Well‐functioned photovoltaics based on nanofibers composed of PBDT‐TIPS‐DTNT‐DT and graphenic precursors thermally modified by polythiophene,polyaniline and polypyrrole

Reduced graphene oxide nanosheets modified by conductive polymers including polythiophene (GPTh), polyaniline (GPANI) and polypyrrole (GPPy) were prepared using the graphene oxide as both substrate and chemical oxidant. UV–visible and Raman analyses confirmed that the graphene oxide simultaneously produced the reduced graphene oxide and polymerized the conjugated polymers. The prepared nanostructures were subsequently electrospun in mixing with poly(3‐hexylthiophene) (P3HT)/phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) and poly[bis(triisopropylsilylethynyl)benzodithiophene‐bis(decyltetradecylthien)naphthobisthiadiazole] (PBDT‐TIPS‐DTNT‐DT)/PC₇₁BM components and embedded in the active layers of photovoltaic devices to improve the charge mobility and efficiency. The GPTh/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM devices demonstrated better photovoltaic features (J_sc = 11.72 mA cm^?2, FF = 61%, V_oc = 0.68 V, PCE = 4.86%, μ_h = 8.7 × 10^?3 cm² V^–1 s^?1 and μ_e = 1.3 × 10^?2 cm² V^–1 s^?1) than the GPPy/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.30 mA cm^?2, FF = 60%, V_oc = 0.66 V, PCE = 4.08%, μ_h = 1.4 × 10^?3 cm² V^–1 s^?1 and μ_e = 8.9 × 10^?3 cm² V^–1 s^?1) and GPANI/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.48 mA cm^?2, FF = 59%, V_oc = 0.65 V, PCE = 4.02%, μ_h = 8.6 × 10^?4 cm² V^–1 s^?1 and μ_e = 7.8 × 10^?3 cm² V^–1 s^?1) systems, assigned to the greater compatibility of PTh in the nano‐hybrids and the thiophenic conjugated polymers in the bulk of the nanofibers and active thin films. Furthermore, the PBDT‐TIPS‐DTNT‐DT polymer chains (3.35%–5.04%) acted better than the P3HT chains (2.01%–3.76%) because of more complicated conductive structures. © 2019 Society of Chemical Industry     

Effect of particle size on the optical properties of lead zirconate titanate nanopowders

Nanopowder samples of lead zirconate titanate (Pb_1.1Zr_0.52Ti_0.48O₃ or PZT) were prepared by the sol‐gel method with controlled pH values. The samples were characterized using FTIR spectroscopy, XRD, FE‐SEM, and TEM techniques. Most of the peaks in the XRD pattern were related to the coexistence of tetragonal‐rhombohedral phases and confirmed the formation of PZT with a perovskite structure. Also, the crystallite size of PZT nanopowders was in a range of 17‐28 nm. FTIR spectroscopy revealed a longitudinal optical (LO) and transverse optical (TO) phonon modes corresponding to the stretching vibration of Ti‐O and Zr‐O bonds. The influence of pH values on the LO and TO phonon modes, LO‐TO splitting, refractive index n(ω), extinction coefficient k(ω), and the real ?₁(ω) and imaginary ?₂(ω) parts of dielectric function was discussed. These properties were investigated in the mid‐infrared region (450‐750 cm^?1). The energy loss function Im[?1/(?)] of PZT nanopowders was obtained by Kramers‐Kronig dispersion relations. The TO phonon frequency decreases with increasing crystallite size of the PZT samples. This effect does not happen at pH 8 to pH 9. As the crystallite size increased from 17.26 nm (at pH 5) to 27.25 nm (at pH 7), the LO‐TO splitting increased as well. This result showed that the optimum pH for absorption of IR radiation and optical application was at pH 7.     

The Role of MgAl2O4 Powder Packing on Phase Stability of Hydroxyapatite During Sintering

MgAl₂O₄ (spinel) was utilized as a packing powder in the sintering of hydroxyapatite (HAp) and the composite of HAp/3 mol% Y₂O₃‐stabilized tetragonal zirconia (3Y‐TZP). The influence of spinel on phase stability of HAp was investigated using X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and electron probe microanalysis (EPMA) to reveal the reaction in the vicinity of the interface between HAp and spinel. When covered with spinel powder, decomposition temperatures for both HAp monolith and HAp in the composite were raised from 1360°C to 1470°C and from 930°C to 1280°C, respectively. SEM images supported the role of spinel on retardation of the decomposition, showing a dense cross section of the monolith after sintering for 2 h at 1400°C with the spinel as opposed to a porous feature without the covering. XRD results indicated that the increase in the decomposition temperatures was accompanied by a decrease in the a‐axis dimension of the hexagonal structure of HAp, probably as a result of the substitution of F^? for OH^?. EPMA revealed that negligible reaction occurred between HAp and spinel even at 1500°C, but the Ca²⁺ in HAp diffused about 20 μm into 3Y‐TZP to form a cubic zirconia solid solution at 1275°C, resulting in the decomposition. The involvement of F^? ion in the contraction of a‐axis parameter and the consequent phase stability were manifested by an increase in the Raman band of the symmetric stretching of the P–O bonds at 962.3 cm^?1 and the appearance of a band for fluoroapatite at 3538 cm^?1.