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Rare-earth (RE)-doped tungstate LiSrGd1−x(WO4)3:xEu red-emitting phosphors were prepared by traditional high-temperature solid-state reaction method. These samples were characterized by X-ray diffraction, scanning electron microscopy, and photoluminescence (PL). PL spectrum exhibited characteristic luminescent 5D0/7FJ (J = 0–4) intra-4f shell Eu3+ ion transitions. Eu3+-activated LiSrGd(WO4)3 phosphors could be excited by near-ultraviolet (NUV) light of 393 nm and blue light of 464 nm and showed excellent red emission lying around 616 nm (5D0 → 7F2). Eu3+-doped concentration in LiSrGd1−x(WO4)3:xEu was x = 0.3. Arising temperature to 393 K, the red emission intensity of LiSrGd1−x(WO4)3:xEu phosphor decayed by only 13.57 and 19.53 $$\%$$ relative to room temperature, which indicates that the phosphor possesses good temperature stability. The evaluated Commission International de l’Eclairage (CIE) color coordinates of these phosphors were close to the standard red CIE color coordinate published by the National Television Systems Committee. Hence LiSrGd1−x(WO4)3:xEu phosphor is promising with potential for white LED.

Relaxation makes ferroelectrics a critical component in sensors, actuators and ultrasound devices, with large electromechanical coupling effects. Although various studies of ferroelectric relaxation have been undertaken, much remains to be investigated regarding the related the properties and mechanisms, with limited studies involving low frequency relaxation characteristics. In this study, an alternative mechanical method using a dynamic mechanical analyzer (DMA) was applied to investigate the low frequency relaxor behavior of PZT-4 ceramics, compared with conventional electric method. Ferroelectric to paraelectric phase transitions were clearly detected and an obvious low frequency relaxor behavior was characterized, induced by Debye relaxation. Then, the activation energy of each relaxation peak and relaxation limit time was theoretically analyzed using the Arrhenius relationship. In addition, the switching of 90° domains was shown to be responsible for relaxor behavior. In contrast, no low frequency relaxor behavior was detected by dielectric measurements, which meant that the mechanical method was more sensitive to internal structural changes. This study deepened the current knowledge on relaxor ferroelectrics, and offered the potential for provide new insights into the investigation of low frequency relaxor characterization.

For optical temperature sensor, high luminescence intensity is as important as high temperature sensing sensitivity. In this work, research on rare-earth ions Er3+/Yb3+ codoped KY(WO4)2–K2WO4 multiphase phosphors for optical temperature sensing application was first proposed by material design. Under a 980 nm excitation, the upconversion luminescence intensity of multiphase materials was much higher than that of pure phase materials. For the 0.6KYW–0.4KW multiphase material, excellent temperature sensing property that the maximal sensitivity was 14.7 × 10− 3 K−1 at 643 K in a broad temperature range from 83 to 663 K was simultaneously obtained. These results indicate that KY(WO4)2–K2WO4 multiphase phosphors with excellent upconversion luminescence and temperature sensing properties are promising candidates for optical temperature sensors.

Asymmetrical equivalent circuits, making φmH as magnetic part for the direct magnetoelectric (DME) effect of magnetoelectric laminate composites of longitudinally magnetized and poled (L–L) mode, have been reported recently. In this paper, we developed a symmetrical magnetic–mechanical–electric equivalent circuit to study both the DME and converse magnetoelectric (CME) effects equivalently, predicting the DME and CME coefficients near the resonance frequency. The theoretical values are in good agreement with the corresponding experiments. The L–L mode laminate composites have higher DME voltage coefficient and CME coefficient in comparison with the longitudinally magnetized and transversely poled (L–T) mode. In particular, its voltage coefficient is almost ten times as large as that of the L–T mode composite. The results are significant for the fabrication of magnetoelectric transducer, energy capture device, electronically controlled magnetometers and magnetic field sensors.

In this article, (Al1−0.02−xSi0.02Tix)2Oy (x = 0.2, 0.9 and 2%) thin films were prepared on Pt/Ti/SiO2/Si substrates using sol–gel technique. The dielectric properties of undoped and Si–Ti co-doped Al2O3 thin films were investigated. The leakage current of (Al0.971Si0.02Ti0.009)2Oy thin film is reduced by 2 orders of magnitude compared with Al2O3 film. Meanwhile, the modified sample exhibits the ultrahigh energy density of 14.01 J/cm3 under the breakdown strength of 647 MV/m, which is an enhancement of 11.26 J/cm3 over that of the undoped Al2O3 film. The improvement of dielectric properties is ascribed to the forming of Al–O–Si, Al–O–Ti bonds and the anodic oxidation of Ti3+, which could strengthen the stability of Al2O3 structure and self-repair the defects of the films under applied electric field. Another reason is that cation vacancies generated by Si–Ti co-doping could effectively prevent the formation of oxygen vacancies and decrease the breakdown probability of the films. This work provides a promising route to dielectric thin films materials for electrical energy storage applications.

Alumina is the great potential material for the high-energy-storage application. Annealing temperature, ambient humidity and temperature are crucial parameters for further investigations of alumina dielectrics. Highly dense and uniform amorphous alumina thin films were prepared by sol–gel and spin-coating technology. The effects of annealing temperature, relative ambient humidity and temperature on dielectric properties of amorphous alumina thin films were first investigated. The annealing temperature varied from 450 to 700 °C. The ambient humidities of 20, 40, 60 and 80% were chosen. The leakage current density of film annealed at 450 °C showed strong dependence on the ambient humidity. However, the effect of ambient humidity on leakage current density weakened as the annealing temperature rising. At the constant ambient humidity, films annealed at 450 and 500 °C showed lower leakage current densities than films annealed at 600 and 700 °C. The various annealing temperatures made little influence on dielectric loss but can enhance slightly the dielectric constant at 500 °C. The annealing temperature of 500 °C was reasonable and the resulting films exhibited stable conduction mechanism at various ambient temperatures. Moreover, the annealing temperature, ambient humidity and temperature did not make the remarkable influence on the breakdown strength.

A novel green emitted phosphor Li2Sr1−xBaxSiO4:Eu2+ (LSBS:Eu) has been synthesized by a solid-state reaction method. Its crystal structure and grain morphology have been investigated by a powder X-ray diffractometer and a scanning electronic microscope, respectively. A green emission peak around 566 nm was observed under the excitation ranged from 225 to 500 nm, which covers the emission spectra of blue and near UV LEDs. The optimal emission intensity was obtained when the Ba content was 0.6 and Eu2+ doping level was 0.003 mol. Furthermore, the investigation of the temperature dependence of luminescence and quantum efficiency indicate that LSBS:Eu phosphors are highly thermally stable and energy saving. The lifetime decay curves and chromaticity coordinates were also obtained. The results show that Li2Sr1−xBaxSiO4:Eu2+ would be a promising green phosphor candidate for UV-chip-based multiphosphor converted white LEDs.

Amorphous SrTiO3 thin films were fabricated on Pt (100)/Ti/SiO2/Si substrates by sol–gel and spin-coating technology and their surface and cross-section morphology were characterized by using field emission scanning electron microscopy. A broad absorption band at about 3390 cm−1 owing to the stretching vibrations of hydroxyl groups in the absorbed water was observed from fourier transform infrared spectroscopy. J–E measurements were used to investigate the electrical characteristics of SrTiO3 films. The breakdown characteristics and leakage current are strongly dependent upon their electrode materials. SrTiO3 films with Al top electrodes exhibit significantly higher breakdown strength and much lower leakage current than those with Au top electrodes. Moreover, samples with Al electrodes exhibit distinct electrical characteristics when a negative voltage was applied under different testing conditions. The surface chemical state of aluminum was analyzed by using X-ray photoelectron spectroscopy, indicating that the 45 nm thick Al electrode was completely transformed into aluminum oxide layer when a positive voltage was applied. These results show that the anodic oxidation of the Al electrodes and films is suggested to be responsible for the enhanced electrical characteristics of SrTiO3 thin films.

When the valve metal is used as anode material, the dielectric properties of sol–gel-derived thin film are greatly enhanced. That is because anodized self-healing occurs at the interface of the anode and the thin film. An oxide insulating layer with a good dielectric property is generated. Anodization heals the defects and the breakdown spots of thin film. Other than anodized self-healing, electrode contact is also an important factor, affecting the dielectric characteristics of the thin film capacitor, which cannot be ignored, especially when both factors exist in one film device. In this study, the sol–gel-derived strontium titanate thin film is used as dielectric material in the film capacitor, and platinum and aluminum as electrode materials. We find that the Schottky barrier at the interface of platinum and strontium titanate greatly reduces the leakage current. However the interface barrier restricts the anodizing of aluminum electrode and the further enhancement of the dielectric strength of the thin film capacitor.

Crystallization processes of sol–gel derived SrTiO3 films have been investigated systematically. The crystallization processes included two stages, firstly, the coordination of the cations changed from the carboxylate groups to the carbonate groups; secondly, the resulting pervskite SrTiO3 was crystallized by the decomposition of the carbonate groups. The intermediate with carbonate groups has also been observed in the SrTiO3 films annealed at 500 °C by the Raman peak shift near 1071 cm−1. The stoichiometry of the intermediate, close to Sr2Ti2O5CO3, has been further confirmed by the TG-DSC and XPS results.

Highly homogeneous and dense Mg-doped Al2O3 films were prepared using sol–gel method. Similar trends occur in the current–voltage characteristics of Al1−xMgxO3−δ series (x = 0, 0.5, 2 and 10 %) films, while 7.7 and 33.3 % Mg-doped Al2O3 films exhibit different trends, and the 33.3 % Mg-doped Al2O3 films have the lowest leakage current, which almost linearly increases with the applied voltage. The dielectric strength of the Al1−xMgxO3−δ series (x = 0.5, 2 and 10 %) films are slightly lower than that of undoped Al2O3 films, while the 7.7 and 33.3 % Mg-doped Al2O3 films possess higher dielectric strength than the undoped Al2O3 films. The Ohmic conduction dominates the leakage current of Al1−xMgxO3−δ (x = 0, 7.7 and 33.3 %) films under lower electric field, while the space-charge-limited-current and Schottky emission, and even other conduction mechanisms, could co-exist under higher electric field.

Amorphous Yttrium-doped aluminum oxide thin films were deposited on Pt/Ti/SiO2/Si substrates by sol–gel. It was observed by field emission scanning electron microscope that the surface morphology was smooth and homogeneous. From Fourier Transform Infrared Spectroscopy, a broad absorption band at 700–1000 cm−1 owing to vibrations of aluminum oxide was observed. The absorption peaks strength relating to hydroxyl group decreased with the increase of Y doping concentration. The electrical properties were investigated in terms of Y doping content and relative humidity. The results show that the existence of hydroxyl and absorbed water makes a significant influence on the electric properties of films. The electric conduction characteristics and dielectric breakdown properties are modified by the decrease of content of hydroxyl and absorbed water, leading to a lower leakage current and higher dielectric strength. It can be seen that the leakage current of films decreases with the Y doping, and could be reasonably deduced that leakage current can be effectively tuned by Y doping.

Aurivillius oxide Na0.5Bi2.5Ta2O9 inserted by Na0.5Er0.5TiO3 ((1 − x)NBTa-xNET, x = 0, 0.05, 0.1, 0.2, 0.3, 0.5) was synthesized by the conventional solid-state method. The ceramic samples with moderate addition of Na0.5Er0.5TiO3 showed strong green and red emissions under 980 nm radiation excitation at room temperature. In the up-conversion luminous spectra, the sample of x = 0.3 had the strongest green emission. Study on how up-conversion luminous intensity varying with excitation power indicated that the green and red up-conversion luminescence (UCL) were both two-photon absorption processes. The dependence of luminescence intensity on temperature was measured in the temperature range of 83–583 K. It was observed that the fluorescence intensity ratio R(I533.6/I546.8) changed with temperature. The maximum temperature sensitivity was found to be about 20.2 × 10−4 K−1 (425 K). It is believed that Er3+ doped in Na0.5Bi2.5Ta2O9 by the form of perovskite-structured Na0.5Er0.5TiO3 is an effective method to improve the UCL property of this ceramic, which has potential application in optical temperature sensor.

Dielectric breakdown behavior of sol–gel derived SrTiO3 films has been studied systematically. The dielectric strength and leakage characteristics of SrTiO3 films were observed to have a strong dependence on the top electrode materials. Compared with films with Ti or Al electrode, SrTiO3 films with Au electrode exhibited relatively low dielectric breakdown strength. Simultaneously, a broad area of damage occurred in the Au electrode after breakdown, which is closely related to the self-healing breakdown mechanism. The corresponding leakage current kept the same order of magnitude when the electric field was higher than 100 MV/m. The higher dielectric strength of the films with Ti or Al electrode is attributed to anodic oxidation of metal electrode.

The Tm3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 (NBT–BT:Tm3+/Yb3+) ceramics were synthesized by solid-state reaction and characterized by X-ray diffraction, SEM, luminescence, dielectric, ferroelectric and piezoelectric measurements. The XRD and SEM showed that all the ceramics were the single phase with perovskite structure. The up-conversion emissions located at 490 nm (blue, 1G4 → 3H6), 551 nm (green, 3F3 → 3H6) and 665, 699 nm (red, 1G4 → 3F4, 3F2 → 3H6). Furthermore, two-photon absorption process would dominate the optimized UC emission intensity in NBT–BT:0.005Tm3+/0.02Yb3+ samples. Moreover, up-conversion temperature sensitivity was detected at NBT–BT:0.005Tm3+/0.02Yb3+ samples with value of 0.068 K−1 related to the intensity ratio of I669 and I665 emissions. In addition, relatively good dielectric properties and ferroelectric properties (Pr = 60 µ/cm2 and Ec = 42 kV) were obtained in NBT–BT:0.005Tm3+/0.005Yb3+. Curie temperature enhanced with large amount of Yb3+ ions increasing (y > 0.02). As multi-functional material, NBT–BT:Tm3+/Yb3+ ceramics may be useful in high temperature electro-optical devices.

In this work, CdO–Bi2O3–PbO–ZnO–Al2O3–B2O3–SiO2 low softening point glass powders were prepared and employed as sintering aid to improve the dielectric breakdown strength and reduce the sintering temperature of Pb0.97La0.02(Zr0.56Sn0.35Ti0.09)O3 antiferroelectric ceramics. The effects of glass content and sintering temperature on the densification, microstructure, dielectric properties and energy storage performance of Pb0.97La0.02(Zr0.56Sn0.35Ti0.09)O3 antiferroelectric ceramics have been investigated. With inclusion of glass, sintered densities comparable to those obtained by conventional sintering are achieved at only 1,050 °C. The breakdown strength of glass-added samples was notably improved due to the reduction of the grain size. The antiferroelectric to ferroelectric switching field and the ferroelectric to antiferroelectric field both increased with increasing glass content. The dielectric constant and dielectric loss decreased gradually with increasing glass content. As a result, the highest recoverable energy density of 3.3 J/cm3 with an energy efficiency of 80 % was achieved in 4 wt% glass-added sample sintered at 1,130 °C.

(1−x) Ba0.5Sr0.5TiO3–xMgMoO4 (x = 0, 5, 10, 20 and 30 wt%) composite ceramics were prepared via solid state reaction processing. Their structure and dielectric properties were systematically characterized. The introduction of MgMoO4 resulted in a change in lattice constant of the perovskite phase and partial reaction between MgMoO4 and Ba0.5Sr0.5TiO3 occurred in the sintering process. Both X-Ray Diffraction (XRD) and Back-scattered Electron Images (BEI) analysis show the co-existence of three phase structures of BST, MgMoO4 and BaMoO4. With increasing of MgMoO4 content, the tunability of the composite ceramics was decreased due to the increase of the amount of non-ferroelectric phases. The Curie temperature Tc of the samples gradually shifted to low temperatures with increasing of MgMoO4 content. Dielectric constant can be adjusted in the range from 2035 to 150, meanwhile maintain a relatively high tunability and Q values. The sample with 20 wt% MgMoO4 possesses a tunability of 10 %, a low dielectric constant of 111 and an appropriate Q value of 183 (2.240 GHz), which meet the requirements of high power and impedance matching, thus making it a promising candidate for applications as electrically tunable microwave devices.

(1−x)(0.36BiScO3–0.64PbTiO3)–xLiNbO3 (BSPT64–xLN) high-temperature relaxor ferroelectric ceramics near the morphotropic phase boundary (MPB) composition were investigated. X-ray diffraction showed a change in symmetry from MPB phase to rhombohedral phase with LiNbO3 content increasing. A change from normal ferroelectric features to relaxor ferroelectric features was observed with LiNbO3 substitution up to x = 0.06, while high-temperature dielectric relaxation was exhibited at T max ~230 to 383°C for 0.02 ≤ x ≤ 0.06. The BSPT64–xLN ceramics with x = 0.02 LiNbO3 exhibited good piezoelectric properties compared with BS–0.64PT ceramics: piezoelectric coefficients d 33 = 505pC/N, planar electromechanical coupling factors k p = 0.47, and remnant polarization P r = 40 μC/cm2, respectively. The annealing temperature dependence of piezoelectric response for BSPT64–xLN ceramics was measured and it was found that the piezoelectric properties decreased slightly before 210°C for x = 0.02 and 0.04, showing excellent thermal stability, which indicated that BSPT64–xLN relaxor ferroelectric ceramics can be used in the range of high temperature compared to Pb-based relaxor ferroelectrics.

Femtosecond laser pulse directly writing microholes by the matrix microholes ablation technique (MMAT) in a high permittivity microwave ceramic Bi(Nb0.998V0.002)O4 were systematically investigated. The feasible micro-fabricating parameters-output power intensity, writing intervals ΔR and step depth ΔZ, and writing velocity-were discussed and optimized. A large scale crystalline wires array at several hundred nanometers induced by multi-photon absorption was observed and analyzed. The tropism of nanometer array was similar to the epitaxy technique but perpendicular to the writing path. The experiment demonstrated the flexibility and efficiency to micro-fabricated superfine and complex configurations in ceramic materials by femtosecond laser.

Temperature stable high-K LTCC material was prepared. The influence of fabrication process on the crystalline phases, microstructures and microwave dielectric properties of TiO2-Bi2O3-CuO ceramics were investigated. The crystalline phases and microstructures of TiO2-Bi2O3-CuO ceramics were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. It was found that rutile TiO2 phase and Bi2Ti4O11 phase co-existed in the TiO2-Bi2O3-CuO ceramics. Separate TiO2 grains and Bi2Ti4O11 grains distributed uniformly in the ceramic matrix. The composition 0.92TiO2-0.08Bi2Ti4O11 with 2 wt% CuO addition that was sintered at 900 °C for 2 h showed high dielectric constant (er ~ 81), high quality factor (Q × f ~ 3,500 GHz) and near zero temperature coefficient of resonant frequency (τf ~ −5.1 ppm/°C), meanwhile the compatibility test showed that it could co-fire with silver electrode. The processing-microstructure-property interrelationship was also studied.

Low-temperature sintered Ca2Zn4Ti15O36 microwave dielectric ceramic was prepared by conventional solid state reaction method. The influences from V2O5 addition on the sintering behavior, crystalline phases, microstructures and microwave dielectric properties were investigated. The crystalline phases and microstructures of Ca2Zn4Ti15O36 ceramic with V2O5 addition were investigated by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). V2O5 addition lowered the sintering temperature of Ca2Zn4Ti15O36 ceramics from 1140 °C to 930 °C. Ca2Zn4Ti15O36 ceramic with 5wt% V2O5 addition could be densified well at 930 °C, and showed good microwave dielectric properties of er ~ 46, Q × f ~ 13400 GHz, and temperature coefficient of resonant frequency (τf) ~ 164 ppm/°C.

The effects of B2O3–CuO (BCu, the weight ratio of B2O3 to CuO is 1:1) addition on the sintering behavior, microstructure, and the microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 (LNT) ceramics have been investigated. The low-amount addition of BCu can effectively lower the sintering temperature of LNT ceramics from 1125 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 2 wt% BCu-added ceramic sintered at 900 °C has better microwave dielectric properties of e r = 50.1, Q × f = 8300 GHz, τ f = 35 ppm/°C. Silver powders were cofired with the dielectric under air atmosphere at 900 °C. The SEM and EDS analysis showed no reaction between the dielectric ceramic and silver powders. This result shows that the LNT dielectric materials are good candidates for LTCC applications with silver electrode.

A new Li2O–Nb2O5–TiO2 (LNT) ceramic with the Li2O:Nb2O5:TiO2 mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li2TiO3 and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li2O–0.17V2O5 (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of er = 51.3, Q × f = 7235 GHz, τ f = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.

A low-temperature plasma-enhanced chemical vapour deposition (PECVD) technique has been employed to produce ultrafine tin oxide powders. The structural features and phase transition of this material have been characterized using differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction, infrared spectroscopy (IR) and transmission electron microscopy (TEM). The oxygen absorption behaviour and gassensing properties have been investigated by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and electrical measurements. Thick film gas sensors made from such ultrafine SnO2 powders yield better sensitivities than those of normal undoped SnO2 gas sensors. A gas-sensing reaction mechanism is also proposed.