Ba2+、MoO42-掺杂对NaCaPO4：Eu3+荧光粉发光性能的影响研究

为提高红色荧光粉的发光强度和色纯度,以硝酸钙、硝酸钠、硝酸铕、磷酸二氢铵、钼酸铵、硝酸钡为原料,采用高温固相法合成了NaCa_1-xPO₄：xEu³⁺、NaCa_1-x（PO₄）_1-y（MoO₄）_y：xEu³⁺、NaCa_1-x-zPO₄：xEu³⁺,zBa²⁺系列红色荧光粉。探讨了Eu³⁺单掺杂和Eu³⁺/MoO₄^2-、Eu³⁺/Ba²⁺共掺杂对荧光粉发光性能的影响。用X射线衍射（XRD）、荧光分光光度计、色坐标等对荧光粉的结构进行表征。研究结果表明：掺杂Eu³⁺、MoO₄^2-、Ba²⁺后NaCaPO₄晶系没有发生变化,但是晶胞参数发生了变化,说明Eu³⁺、MoO₄^2-、Ba²⁺进入NaCaPO₄晶格中。在393 nm紫外光激发下,荧光粉发射光谱图出现两个Eu³⁺比较强的特征发射峰,分别属于Eu³⁺的⁵D₀→⁷F₁和⁵D₀→⁷F₂跃迁。与单掺杂16%Eu³⁺荧光粉相比,共掺杂16%Eu³⁺/3%MoO₄^2-或16%Eu³⁺/6%Ba²⁺荧光粉的发射光谱中⁵D₀→⁷F₂跃迁产生的发射峰强度均高于单掺杂16%Eu³⁺荧光粉的发射峰强度,其⁵D₀→⁷F₂与⁵D₀→⁷F₁发射光强度之比（R）分别为1.76（R_Mo）和1.28（R_Ba）,都大于单掺杂16%Eu³⁺荧光粉的R_Eu（0.99）,共掺杂Eu³⁺/MoO₄^2-荧光粉的色纯度比单掺杂Eu³⁺和共掺杂Eu³⁺/Ba²⁺荧光粉的色纯度更好。     

Luminescent properties of Pr doped ZrSiO4 phosphors

Mixtures of ZrO₂, SiO₂, Pr₂O₃, and H₃BO₃ were fired at the temperature of 1150–1350 °C under H₂ atmosphere. A single phase ZrSiO₄:Pr phosphors could be achieved at the firing temperature above 1150 °C. Crystallinity and PL properties strongly depended on the flux amounts, firing temperature, and dopant concentrations. ZrSiO₄:Pr phosphors showed a strong red emission at 615 nm and a weak red emission at 622 nm with an excitation wavelength of 295 and 450 nm, respectively. Two sets of the emission bands and excitation spectra originated from Pr³⁺ ions at Zr and Si sites, respectively.     

Plasma-electrochemical synthesis of europium doped cerium oxide nanoparticles

In the present study,a plasma-electrochemical method was demonstrated for the synthesis of europium doped ceria nanoparticles.Ce(NO3)3· 6H2O and Eu(NO3)3·5H2O were used as the starting materials and being dissolved in the distilled water as the electrolyte solution.The plasma-liquid interaction process was in-situ investigated by an optical emission spectroscopy,and the obtained products were characterized by complementary analytical methods.Results showed that crystalline cubic CeO2:Eu3+ nanoparticles were successfully obtained,with a particle size in the range from 30 to 60 nm.The crystal structure didn't change during the calcination at a temperature from 400℃ to 1000℃,with the average erystallite size being estimated to be 52 nm at 1000℃.Eu3+ ions were shown to be effectively and uniformly doped into the CeO2 lattices.As a result,the obtained nanophosphors emit apparent red color under the UV irradiation,which can be easily observed by naked eye.The photoluminescence spectrum further proves the downshift behavior of the obtained products,where characteristic 5Do → 7F1,2,3 transitions of Eu3+ ions had been detected.Due to the simple,flexible and environmental friendly process,this plasma-electrochemical method should have great potential for the synthesis of a series of nanophosphors,especially for bio-application purpose.     

Solid state protonic conductor NH4PO3–(NH4)2Mn(PO3)4 for intermediate temperature fuel cells

A new proton-conductive composite of NH₄PO₃–(NH₄)₂Mn(PO₃)₄ was synthesized and characterized as a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C. Thermal gravimetric analysis and X-ray diffraction investigation showed that (NH₄)₂Mn(PO₃)₄ was stable as a supporting matrix for NH₄PO₃. The composite conductivity, measured using impedance spectroscopy, improved with increasing the molar ratio of NH₄PO₃ in both dry and wet atmospheres. A conductivity of 7 mS cm⁻¹ was obtained at 250 °C in wet hydrogen. Electromotive forces measured by hydrogen concentration cells showed that the composite was nearly a pure protonic conductor with hydrogen partial pressure in the range of 10²–10⁵ Pa. The proton transference number was determined to be 0.95 at 250 °C for 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte. Fuel cells using 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ as an electrolyte and the Pt–C catalyst as an electrode were fabricated. Maximum power density of 16.8 mW/cm² was achieved at 250 °C with dry hydrogen and dry oxygen as the fuel and oxidant, respectively. However, the NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte is not compatible with the Pt–C catalyst, indicating that it is critical to develop new electrode materials for the intermediate temperature fuel cells.     

Effect of codoping LiNbo3:Eu3 crystal with Mg2 ions on the Eu3 optical absorption spectrum

In this work the optical absorption spectra of Eu³⁺ doped LiNbO₃ measured as a function of Li/Nb ratio are presented. Two Eu³⁺ sites, dealing with the Nb⁺⁵ and Li⁺ lattice sites, have been characterized by their corresponding ⁷F_o -⁵D₂ optical transitions. A doubly doped sample (LiNbo³: Mg, Eu) has been used to study the influence of Mg²⁺ ions on the Eu³⁺ optical absorption spectrum. The main effect is a shifting of the relative occupation of the two Eu³⁺ sites.     

High-quality, oriented and mesostructured organosilica monolith as a potential UV sensor

We synthesized high-quality and oriented periodic mesoporous organosilica (PMO) monoliths through a solvent evaporation process using a wide range of mole ratios of the components: 0.17–0.56 1,2-bis(triethoxysilyl)ethane (BTSE): 0.2 cetyltrimethylammonium chloride (CTACl): 0–1.8 × 10⁻³ HCl: 0–80 EtOH: 5–400 H₂O. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images indicated that the mesoporous channels within the monolith samples were oriented parallel to the flat external surface of the PMO monolith and possessed a hexagonal symmetry lattice (p6mm). The PMO monolith synthesized from a reactant composition of 0.35 BTSE: 0.2 CTACl: 1.8 × 10⁻⁶ HCl: 10 EtOH: 10 H₂O had a pore diameter, pore volume, and surface area – obtained from an N₂ sorption isotherm – of 25.0 Å, 0.96 cm³ g⁻¹ and 1231 m² g⁻¹, respectively. After calcination at 280 °C for 2 h in N₂ flow, the PMO monolith retained monolith-shape and mesostructure. Pore diameter and surface area of the calcined PMO monolith sample were 19.8 Å, 0.53 cm³ g⁻¹ and 1368 m² g⁻¹, respectively. We performed ²⁹Si and ¹³C CP MAS NMR spectroscopy experiments to confirm the presence of Si–C bonding within the framework of the PMO monoliths. We investigated the thermal stability of the PMO monoliths through thermogravimetric analysis (TGA). In addition, rare-earth ions (Eu³⁺, Tb³⁺ and Tm³⁺) were doped into the monoliths. Optical properties of those Eu³⁺, Tb³⁺ and Tm³⁺-doped PMO monoliths were investigated by photoluminescence (PL) spectra to evaluate their potential applicability as UV sensors.     

Spectroscopic analysis of carbon dioxide and nitrogen mixed gas hydrates in silica gel for CO2 separation

In this study solid-state NMR spectroscopy was used to identify structure and guest distribution of the mixed N₂ + CO₂ hydrates. These results show that it is possible to recover CO₂ from flue gas by forming a mixed hydrate that removes CO₂ preferentially from CO₂/N₂ gas mixture. Hydrate phase equilibria for the ternary CO₂–N₂–water system in silica gel pores were measured, which show that the three-phase H–L_w–V equilibrium curves were shifted to higher pressures at a specific temperature when the concentration of CO₂ in the vapor phase decreased. ¹³C cross-polarization (CP) NMR spectra of the mixed hydrates at gas compositions of more than 10 mol% CO₂ with the balance N₂ identified that the crystal structure of mixed hydrates as structure I, and that the CO₂ molecules occupy mainly the abundant 5¹²6² cages. This makes it possible to achieve concentrations of more than 96 mol% CO₂ gas in the product after three cycles of hydrate formation and dissociation.     

Synthesis and Photoluminescence Properties of Eu3+-Doped Calcium Phosphates

Eu³⁺-doped (1–12 mol%) calcium hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders were synthesized by a precipitation method and their photoluminescence (PL) properties were investigated. Eu has a limited solubility in HA and Eu₂O₃ was detected by X-ray diffraction above 3% doping, whereas a nearly single β-phase was obtained up to 6% doping in TCP but EuPO₄ appeared in the 12% Eu-doped specimen. Electron spin resonance measurement confirmed that europium ions exist as Eu³⁺ in both samples. Eu³⁺-doped HA exhibited a strong emission at 575 nm with several minor peaks at 610–640 nm and Eu³⁺-doped TCP had an intense emission at 613 nm with secondary peaks at 590–600 nm, which were consistent with the earlier reports determined at low temperatures. In Eu-doped TCP, the PL intensity increased with increasing calcination temperature without phase transformation. The more the Eu added, the higher the PL intensity obtained in both cases.     

Electrical resistivity of transition metal ion doped Mullite

The electrical resistivity of pure mullite (3Al₂O₃.2SiO₂) varies from 10¹³ ohm-cm at room temperature (r.t.) to 10⁴ ohm-cm at 1400 °C. It was observed that by doping mullite with the 3d-type transition metal ions, e.g. Mn, Fe, Cr and Ti, the resistivity of mullite could be reduced to 10¹¹ ohm-cm, i.e. 1/100 that at r.t. and 1/5 that at 1400 °C. The resistivity of doped and undoped mullite decreased by 6–5 orders at about 500–600 °C but 4–3 orders between this temperature and 1400 °C. The 3d orbital electrons, the oxidation states and the concentration of the transition metal ions as well as the sites of mullite lattice occupied by the ions were found responsible for lowering of resistivity of mullite. Evidence of the presence of Mn²⁺, Mn³⁺, Fe³⁺, Cr³⁺ and Ti⁴⁺ ions in mullite had been obtained which entered the octahedral site. The Ti⁴⁺ ion which substituted Al³⁺ ion in the octahedral site of mullite structure appeared to be the most efficient one to reduce the resistivity. This has been confirmed by the results of activation energy of resistivity/band gap energy, Eg which was the lowest for mullite doped with 1·0 wt% Ti⁴⁺ ion. At 1·0 wt% concentration level, these ions lowered the resistivity of mullite to minimum.     

Preparation and characteristics of natural rubber/poly(ethylene oxide) salt hybrid mixtures as novel polymer electrolytes

Poly(ethylene oxide) (PEO) of molecular weight 1000 (PEO₁₀₀₀) containing lithium benzenesulfonate (LiBs) (PEO₁₀₀₀/LiBs), PEO derivatives having benzenesulfonate groups on both chain ends (PEO₁₀₀₀–(BSLi)₂), or 1-ethyl-2,3-dimethylimidazolium bromide (ImB), were each blended with natural rubber (NR). The ionic conductivity was measured from AC impedance values. The ionic conductivity of the mixture of NR and PEO₁₀₀₀/LiBs (40 wt%) was about 10⁻⁶ S cm⁻¹ at 50°C; this mixture retained rubbery physical characteristics. At NR content of 10 wt%, the ionic conductivity of the mixture (NR/PEO₁₀₀₀/LiBs) was 2.7×10⁻⁵ Scm⁻¹ at 50°C, approximately 10 times higher than that of the bulk PEO/LiBs mixture. For mixtures of NR and PEO₁₀₀₀–(BSLi)₂, no improvement in ionic conductivity by mixing was found. The ionic conductivity of the mixture of NR and ImB was about 10 times higher than for the bulk of PEO₁₀₀₀–(BSLi)₂ at a NR content of 10 wt%. We propose that the ionic conductivity of the mixture increases when an ion conducting matrix containing simple salt is added. On the other hand, the DSC curve for NR/PEO derivatives showed two T_gs based on the separate components, suggesting phase separation of the PEO derivative in the NR phase.     

Oxidative degradation properties of Co-based catalysts in the presence of ozone

Four series of cobalt-based catalysts, such as bare Co₃O₄ and CoO, CoO_x–CeO₂ mixed oxides, CoO_x supported over alumina and alumina–baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV–visible diffuse reflectance spectroscopy and TG/DT were performed.

The CoNiAl hydrotalcite exhibits, after 4 h of reaction, the highest phenol ozonation activity followed by Co(3 wt%)/Al₂O₃–BaO and CoMgAl. The samples Co(1 wt%)/Al₂O₃–BaO and Co(1 and 3 wt%)/Al₂O₃ show a comparable medium activity, while the oxidation properties of bare oxides Co₃O₄, CoO and CoO_x–CeO₂ are really low. Leaching of cobalt ions in the water solution was detected during the reaction, the amount varied depending on the nature of catalysts. A massive release was observed for the CoMgAl and CoNiAl hydrotalcites, while cobalt catalysts over alumina and alumina–baria look much more stable. The recycle of CoO_x/Al₂O₃ and CoO_x/Al₂O₃–BaO was studied by performing three consecutive cycles in the phenol oxidation. Because of the potential interest of the cobalt-supported catalysts in the ozonation process, the oxidative degradation of naphtol blue black was also investigated.

On the basis of TPR and UV–visible results it appears that highly dispersed Co²⁺ ions especially present over Co(3 wt%)/Al₂O₃–BaO are the main active sites for phenol and naphtol blue black oxidative degradation by ozone.     

Determination of active palladium species in ZSM-5 zeolite for selective reduction of nitric oxide with methane

The active site in ZSM-5 zeolite-supported palladium, which shows the catalytic activity for NO reduction with methane as a reducing agent, has been investigated qualitatively and quantitatively by means of NO chemisorption and NaCl titration, comparing with PdO supported on silica. Palladium species in 0.4 wt.% Pd loaded H-ZSM-5 can adsorb NO equimolarly after calcination at 773 K, and almost all the NO was desorbed at around 673 K, while the palladium species on PdO/SiO₂ hardly adsorbed NO. The palladium species in Pd(0.4)/H-ZSM-5 are ion-exchangeable with Na⁺ in NaCl solution, indicating that they exist in a cationic state of an isolated Pd²⁺. This method for quantitative analysis of the isolated Pd²⁺ cations is named as ‘NaCl titration’. The amount of the isolated Pd²⁺ cationic species increased with increasing palladium content on Pd/H-ZSM-5, and PdO co-existed above 1 wt.%. The amount of the isolated Pd²⁺ cation was unchanged after the reaction of NO₂–CH₄, NO₂–CH₄–O₂, or CH₄–O₂ at 673 K, while the adsorbed amount of NO per the Pd²⁺ as determined by NO-TPD decreased after the NO₂–CH₄–O₂ reaction. It was found by NaCl titration that the catalytic activity of Pd/H-ZSM-5 for NO₂–CH₄–O₂ reaction increased with increasing amount of the isolated Pd²⁺ cationic species up to 0.7 wt.%, while the increase in the amount of PdO led to decrease in selectivity towards NO₂ reduction. The palladium species that are active and selective for NO reduction with CH₄ will be proposed.     

Piezoelectric properties of Pb(Mn1/3Nb2/3)O3–PbZrO3–PbTiO3 ceramics with sintering aid of 2CaO–Fe2O3 compound

Since the electromechanical devices move towards enhanced power density, high mechanical quality factor (Q_m) and electromechanical coupling factor (k_p) are commonly needed for the high powered piezoelectric transformer with Q_m≥2000 and k_p=0.60. Although Pb(Mn_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ (PMnN–PZ–PT) ceramic system has potential for piezoelectric transformer application, further improvements of Q_m and k_p are needed. Addition of 2CaO–Fe₂O₃ has been proved to have many beneficial effects on Pb(Zr,Ti)O₃ ceramics. Therefore, 2CaO–Fe₂O₃ is used as additive in order to improve the piezoelectric properties in this study. The piezoelectric properties, density and microstructures of 0.07Pb(Mn_1/3Nb_2/3)O₃–0.468PbZrO₃–0.462PbTiO₃ (PMnN–PZ–PT) piezoelectric ceramics with 2CaO–Fe₂O₃ additive sintered at 1100 and 1250 °C have been studied. When sintering temperature is 1250 °C, Q_m has the maximum 2150 with 0.3 wt.% 2CaO–Fe₂O₃ addition. The k_p more than 0.6 is observed for samples sintered at 1100 °C. The addition of 2CaO–Fe₂O₃ can significantly enhance the densification of PMnN–PZ–PT ceramics when the sintering temperature is 1250 °C. The grain growth occurred with the amount of 2CaO–Fe₂O₃ at both sintering temperatures.     

Luminescent poly(1,4-phenylene vinylene-4,4′-biphenylene vinylene)s containing oligo(ethylene oxide) or hexyloxy side groups

Two soluble poly(1,4-phenylene vinylene-4,4′-biphenylene vinylene)s (P1, P2) were synthesized through the Wittig condensation, in which P1 and P2 contain flexible oligo(ethylene oxide) and hexyloxy side groups, respectively. Furthermore, a blend of P1 with lithium perchlorate (P1–LP) was obtained to investigate the effect of doping. The polymers show good solubility in common organic solvents and are thermally stable (T_d>315 °C). The optical properties of the polymers, both in solution and as cast films, were investigated by absorption and photoluminescence (PL) spectra, whereas the electrochemical characteristics were obtained using cyclic voltammetric measurement. The LUMO levels of P1, P2, and P1–LP are −3.18, −3.21 and −3.79 eV and the band-gaps are 1.95, 2.18, and 1.27 eV, respectively. Double-layer light-emitting diodes (ITO/PEDOT/Polymer/Al) were successfully fabricated to investigate their electroluminescent (EL) properties. The PL and EL spectral maxima of P1, P2, and P1–LP locate at 507–509 nm and 511–516 nm, indicating that they are yellowish-green emitting materials. The turn-on electric field was 4.2×10⁵, 5.6×10⁵, and 3.4×10⁵ V/cm and maximum luminance was 175, 268, and 620 cd/m² for P1, P2, and P1–LP, respectively.     

Visible light photocatalysis on praseodymium(III)-nitrate-modified TiO2 prepared by an ultrasound method

Nanocrystalline TiO₂ incorporated with praseodymium(III) nitrate has been prepared by an ultrasound method in a sol–gel process. The prepared sample is characterized by X-ray diffraction (XRD), nitrogen adsorption (BET surface area), UV–vis diffuse reflectance spectroscopy (UV–Vis DRS) and X-ray photoelectron spectroscopy (XPS). The prepared material consists of TiO₂ nanocrystalline with 5 nm size incorporated with highly dispersed Pr(NO₃)₃. Visible light absorptions at 444, 469, 482 and 590 nm are observed in the prepared sample. These bands are attributed to the 4f transitions ³H₄ → ³P₂, ³H₄ → ³P₁, ³H₄ → ³P₀ and ³H₄ → ¹D₂ of praseodymium(III) ions, respectively. This sample Pr(NO₃)₃-TiO₂, as a novel visible light photocatalyst, shows high activity and stability in the decomposing rhodamine-B (RhB) and 4-chlorophenol (4-CP) under visible light irradiation. Results examined by electron spin resonance spectroscopy (ESR) reveal that the irradiation (>420 nm) of the photocatalyst dispersed in RhB aqueous solution induces the generation of highly active hydroxyl radicals (OH), leading to the cleavage of the whole conjugated chromophore structure of RhB. A mechanism based on local excitation of praseodymium(III) nitrate chromophore and interfacial charge transfer from the chromophore to TiO₂ is proposed to explain the formation of active hydroxyl radicals in the photocatalytic system under visible light irradiation.     

Rich photoluminescence emission of SnO2–SiO2 composite aerogels prepared with a co-fed precursor sol–gel process

Tin oxide–silica composite aerogels were successfully prepared with a co-fed precursor sol–gel process. The crystallinity of the tin oxide nanoparticles, embedded in the mesoporous SiO₂ network, was improved with increasing the post-reaction thermal treatment temperature. The composite aerogels exhibited a rich photoluminescence (PL) emission contributed by both SnO₂ and SiO₂. The PL peak of 346 nm was from the near band edge emission of the tin oxide nanoparticles, and the ones located at 310 and 476 nm were attributable to the oxygen deficiencies of the silica network. Three more emission peaks, 387, 432, and 522 nm, were observed, with the 387 nm peak contributed by the oxygen vacancies V_O⁺⁺, the 432 nm peak by the Sn interstitials, and the 522 nm peak by the oxygen vacancies V_O⁺, respectively, of the tin oxide nanoparticles. The intensities of these three defect level emissions were found decreased, as compared to that of the near band edge emission, with increasing the post-reaction thermal treatment temperature as the tin oxide crystallinity improved.     

High-rate properties of LiFePO4/carbon composites as cathode materials for lithium-ion batteries

Electrochemical properties of LiFePO₄/carbon composites were investigated to achieve a high-rate lithium electrode performance. LiFePO₄/carbon composites were synthesized by a hydrothermal reaction of a solution of FeSO₄·7H₂O, H₃PO₄, and LiOH·H₂O mixed with carbon powders under nitrogen atmosphere followed by annealing under 1% H₂–99% Ar atmosphere. Particle size of the obtained LiFePO₄/carbon composites observed by scanning electron microscopy was less than 100 nm. At a high current density of 1000 mA g⁻¹, the LiFePO₄/carbon composites showed a high discharge capacity of 113 mA h g⁻¹, and a flat discharge potential plateau was observed around 3.4 V. The discharge capacity at the high current density, 85% of that at a low current density of 30 mA g⁻¹, is a quite high value for LiFePO₄ cathodes. Homogeneous microstructure consisting of small particles contributed to the high-rate properties of the LiFePO₄/carbon composites.     

Low-temperature sintering of 0.85CaWO4–0.15LaNbO4 ceramics

Microwave dielectric properties of 0.85CaWO₄–0.15LaNbO₄ (CWLN) ceramics were investigated as a function of H₃BO₃, Li₂CO₃ content and sintering temperature. With the co-addition of 3.0 wt.% H₃BO₃–1.0 wt.% Li₂CO₃, the sintering temperature could be effectively reduced from 1150 °C for pure CWLN ceramics to 900 °C without any degradation of dielectric properties. These results are due to the enhancement of the sinterability of CWLN by liquid phase sintering. For the specimens with H₃BO₃–Li₂CO₃ sintered at 900 °C for 3 h, the dielectric constant (K) did not changed remarkably. However, the quality factor (Qf) and the temperature coefficient of resonant frequency (TCF) increased up to y = 1.0 of 3.0 wt.% H₃BO₃–y wt.% Li₂CO₃, and then decreased due to the formation of the secondary phases. Typically, K of 11.8, Qf of 45,200 GHz and TCF of −23.1 ppm/°C were obtained for the specimens of CWLN with 3.0 wt.% H₃BO₃–1.0 wt.% Li₂CO₃ sintered at 900 °C for 3 h.     

Piezoelectric properties of low temperature sintering in Pb(Zr,Ti)O3–Pb(Zn,Ni)1/3Nb2/3O3 ceramics for piezoelectric transformer applications

In this study, in order to develop low-temperature sintering ceramics for a multilayer piezoelectric transformer application, we explored CuO and Bi₂O₃ as sintering aids at low temperature (900 °C) sintering condition for Sb, Li and Mn-substituted 0.8Pb(Zr_0.48Ti_0.52)O₃–0.16Pb(Zn_1/3Nb_2/3)O₃–0.04Pb(Ni_1/3Nb_2/3)O₃ ceramics. These substituted ceramics have excellent piezoelectric and dielectric properties such as d₃₃  347 pC/N, k_p  0.57 and Q_m  1469 when sintered at 1200 °C. The addition of CuO decreased the sintering temperature through the formation of a liquid phase. However, the piezoelectric properties of the CuO-added ceramics sintered below 900 °C were lower than the desired values. The additional Bi₂O₃ resulted in a significant improvement in the piezoelectric properties. The composition Sb, Li and Mn-substituted 0.8Pb(Zr_0.48Ti_0.52)O₃–0.16Pb(Zn_1/3Nb_2/3)O₃–0.04Pb(Ni_1/3Nb_2/3)O₃ + 0.5 wt% CuO + 0.5 wt% Bi₂O₃ showed the value of k_p = 0.56, Q_m = 1042 (planar mode), d₃₃ = 350 pC/N, when it was sintered at 900 °C for 2 h. These values indicated that the newly developed composition might be suitable for multilayer piezoelectric transformer application.     

Temperature-dependent dielectric, impedance and tunability studies on bismuth zinc niobate ((Bi1.5Zn0.5)(Nb1.5Zn0.5)O7) ceramics

Bi₂O₃–ZnO–Nb₂O₅-based pyrochlore ceramics are receiving increasing attention due to their excellent dielectric properties in the microwave frequency range. Site disorder at the pyrochlore A-site is well known for lone pair active cations like Bi³⁺ and is attributed as the reason for this material's high dielectric constant and tunability. Bismuth zinc niobate ((Bi_1.5Zn_0.5)(Nb_1.5Zn_0.5)O₇) [BZN] ceramics are prepared by the conventional solid-state reactions. The relative permittivity (_r) and the dielectric loss tangent (tan δ) of the BZN ceramics sintered at 1000 °C are found to be around 130 and 0.0004, respectively at a frequency of 1 MHz measured at room temperature. The impedance spectroscopy measurements are conducted at different temperatures to separate grain and grain boundary contributions to the dielectric constant. The tunability of these ceramics is studied under a constant dc bias voltage.