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1.
Highly oriented tungsten–bronze K(Sr,Ba)2Nb5O15 (KSBN) thin films have been fabricated by a chemical solution deposition method. Alkoxy-derived K(Sr0.5Ba0.5)2Nb5O15 (KSBN50) thin films directly crystallized into a tetragonal tungsten–bronze phase on fused silica, MgO(1 0 0), and Pt(1 0 0)/MgO(1 0 0) substrates with c-axis preferred orientation at 700 °C by optimizing the processing conditions. Ferroelectric KSBN50 thin films on Pt(1 0 0)/MgO(1 0 0) exhibited the diffuse-phase transition and typical relaxor-type dielectric behavior, which are characteristic properties along the c-axis of the tungsten–bronze (Sr,Ba)Nb2O6 crystal. The KSBN thin films synthesized on fused silica and MgO(1 0 0) showed high transparency over a wide wavelength range. The propagation modes of the synthesized KSBN thin films were characterized by the prism coupling method. The values of their refractive indices in TE and TM modes were 2.27 and 2.25, respectively.  相似文献   

2.
《Optical Materials》2014,36(12):2624-2628
β-Ga2O3 films were grown on double-side polished MgAl6O10 (1 0 0) substrate by metal organic chemical vapor deposition (MOCVD) at 600, 650 and 700 °C. The refractive index dispersive behaviors of Ga2O3 films have the typical shape of the normal dispersion curve. Photoluminescence (PL) spectra measured at room temperature revealed that all the films exhibited intense ultraviolet (UV)–green emission from 300 to 650 nm. A minor deep UV emission around 275 nm (∼4.51 eV) was observed for the sample prepared at 700 °C. The intensity of the emission increased markedly when measured at low temperature. The corresponding PL mechanisms were discussed in detail and a schematic diagram was proposed.  相似文献   

3.
Natural-superlattice-structured ferroelectric thin films, Bi3TiNbO9–Bi4Ti3O12 (BTN–BIT), have been synthesized on Pt/Ti/SiO2/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O2 ambient are consisted of iteration of two unit cells of Bi3TiNbO9 and one unit cell of Bi4Ti3O12. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O2 flow rate from 0.5 to 1.5 L/min, both remanent polarization Pr and coercive electric field EC increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O2 ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of Pr = 23.5 μC/cm2 and EC = 135 kV/cm.  相似文献   

4.
Nanoparticles of chromium oxide have been synthesized following a precipitation technique at reaction temperatures 5, 27 and 65 °C. Synthesized powders were characterized using X-ray diffraction, transmission electron microscope and Brunauer–Emmett–Teller techniques to carry out structural and morphological analysis. The reaction temperature has been found to be playing a crucial role in controlling particle size. It has been observed that Cr2O3 nanoparticles synthesized at 27 °C were smaller as compared to those synthesized at 5 and 65 °C. Chromium oxide samples thus prepared were deposited as thick films on alumina substrates to act as gas sensors and their sensing response to ethanol vapour was investigated at different operable temperatures. It has been observed that all the sensors exhibited optimum response at 250 °C. The investigations revealed that sensing response of Cr2O3 nanoparticles synthesized at 27 °C was exceptionally higher than that of Cr2O3 nanoparticles synthesized at 5 and 65 °C.  相似文献   

5.
In the present research, self-cleaning Al2O3–TiO2 thin films were successfully prepared on glass substrate using a sol–gel technique for photocatalytic applications. We investigated the phase structure, microstructure, adhesion and optical properties of the coatings by using XRD, SEM, scratch tester and UV/Vis spectrophotometer. Four different solutions were prepared by changing Al/Ti molar ratios such as 0, 0.07, 0.18 and 0.73. Glass substrates were coated by solutions of Ti-alkoxide, Al-chloride, glacial acetic acid and isopropanol. The obtained gel films were dried at 300 °C for 10 min and subsequently heat-treated at 500 °C for 5 min in air. The oxide thin films were annealed at 600 °C for 60 min in air. TiO2, Ti3O5, TiO, Ti2O, α-Al2O3 and AlTi phases were determined in the coatings. The microstructural observations demonstrated that Al2O3 content improved surface morphology of the films and the thickness of film and surface defects increased in accordance with number of dipping. It was found that the critical load values of the films with 0, 0.07, 0.18 and 0.73 Al/Ti molar ratios were found to be 11, 15, 22 and 28 mN, respectively. For the optical property, the absorption band of synthesized powders shifted from the UV region to the visible region according to the increase of the amount of Al dopant. The oxide films were found to be active for photocatalytic decomposition of methylene blue.  相似文献   

6.
《Materials Letters》2007,61(19-20):4140-4143
Polycrystalline Ba5LnZnNb9O30 (Ln = La, Nd and Sm) ceramics were prepared as single-phase materials through conventional solid-state ceramics route. The structure was characterized by X-ray diffraction methods and scanning electron microscopy (SEM) and the dielectric properties were measured from − 120 °C to 150 °C. All three compounds are paraelectric phases adopting the filled tetragonal tungsten–bronze (TB) structure at room temperature, and the Curie temperature (at 1 MHz) were − 60, − 25 and − 5 °C for Ba5LaZnNb9O30, Ba5NdZnNb9O30, and Ba5SmZnNb9O30 respectively. At 1 MHz their dielectric constant (εr) varies from 258 to 310, dielectric loss (tanδ) from 0.0033 to 0.0068, and the temperature coefficients of the dielectric constant (τε) from − 1220 to − 1390 ppm °C 1.  相似文献   

7.
BaTi2O5 nanobelts with 60–100 nm in thickness, 200–300 nm in width, and several micrometers in length have been successfully synthesized through a two-step hydrothermal reaction. Sodium titanate nanobelts are synthesized via the reaction of titania nanoparticles and NaOH aqueous solution at 180 °C for 24 h. After the reaction, resulting sodium titanate nanobelts are ion-exchanged with barium ions and then treated at 180 °C for 60 h under alkaline condition, BaTi2O5 nanobelts are formed. The morphologies and crystal structures of sodium titanate and BaTi2O5 nanobelts are characterized by field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray powder diffractometer (XRD), respectively.  相似文献   

8.
《Optical Materials》2005,27(3):419-423
Nanocrystalline ZnS films have been prepared by sulfidation of the reactive magnetron sputtered ZnO films. The structure, composition and optical properties of the sulfurized ZnO films as a function of the sulfidation temperature (TS) have been systematically studied. It is found that at TS  400 °C ZnO is completely converted to ZnS with the hexagonal structure. The ZnS films have a strongly (0 0 2) preferred orientation and an optical transparency of about 80% in the visible region. In addition, at TS < 444.6 °C (boiling point of sulfur), some residual sulfur decomposed from H2S gas can adhere to the sulfurized film surface while at TS = 580 °C a S/Zn ratio much higher than the ideal stoichiometric proportion of ZnS is obtained for the ZnS films. ZnS films with a minimum XRD FWHM value of 0.165° and a good S/Zn ratio of 0.99 are obtained at a temperature of 500 °C indicating the ZnS films to be suitable for use in the thin film solar cells.  相似文献   

9.
This study investigates effects of the zinc oxide (ZnO) addition and the sintering temperature on the microstructure and the electrical properties (such as dielectric constant and loss tangent) of the lead-free piezoelectric ceramic of bismuth sodium titanate (Na0.5Bi0.5TiO3), NBT, which was prepared using the mixed oxide method. Three kinds of starting powders (such as Bi2O3, Na2CO3 and TiO2) were mixed and calcined. This calcined NBT powder and a certain weight percentage of ZnO were mixed and compressed into a green compact of NBT–ZnO. Then, this green compact of NBT–ZnO was sintered to be a disk doped with ZnO, and its characteristics were measured. In this study, the calcining temperature was 800 °C, the sintering temperatures ranged from 1000 to 1150 °C, and the weight percentages of ZnO doping included 0.0, 0.5, 1.0, and 2.0 wt%. At a fixed wt% ZnO, the grain size increases with increase in the sintering temperature. The largest relative density of the NBT disk obtained in this study is 98.3% at the calcining temperature of 800 °C, the sintering temperature of 1050 °C, and 0.5 wt% ZnO addition. Its corresponding dielectric constant and loss tangent are 216.55 and 0.133, respectively.  相似文献   

10.
LiMn2O3.9Br0.1 nanoparticles were prepared by a room-temperature solid-state coordination method. The structure and morphology of the as-prepared materials were analyzed by X-ray diffractometry and transmission electron microscopy. The results show that the LiMn2O3.9Br0.1 is well-crystallized and consists of monodispersed nanoparticles 80–100 nm in size. Results of electrochemical testing show that the samples prepared at different temperatures have similar electrochemical performance. The initial discharge capacities of LiMn2O3.9Br0.1 prepared at 800 °C and 700 °C are 121 mAh g? 1 and 118.9 mAh g? 1, respectively, higher than for LiMn2O4 prepared using the same method.  相似文献   

11.
Yttrium silicate (Y–Si–O) films with eggshell- and fur-like microstructures were prepared by laser chemical vapor deposition using a Nd:YAG laser, and tetraethyl orthosilicate (TEOS) and yttrium dipivaloylmethane (Y(dpm)3) precursors. Amorphous Y–Si–O films were prepared at deposition temperature below 1200 K. The crystalline Y–Si–O films with mixtures of Y4.67(SiO4)3O and α-Y2Si2O7 phases were obtained at deposition temperature above 1200 K. y-Y2Si2O7 and X1-Y2SiO5 minor phases were also formed at a higher deposition temperature. At deposition temperature ranging between 1285 and 1355 K, a dome-like structure covered with fine fur-like projections was formed under a total pressure of 3.5 kPa, whereas an eggshell-like structure 200–300 μm in diameter and 10–20 μm in shell thickness was formed at 7.5 kPa. The deposition rate for the Y–Si–O films with fur- and eggshell-like microstructures reached 300 and 1000 μm h?1, respectively.  相似文献   

12.
《Materials Research Bulletin》2006,41(10):1798-1805
A new family of ferroelectric compounds with Ba2−xNa1+xLixNb5O15 composition (0  x  1) and tetragonal tungsten–bronze structure is processed for the first time. This new family of materials derived from Ba2NaNb5O15 compound was processed by classical solid-state reaction and by mechanosynthesis. The powders prepared by these two routes were characterized by X-ray diffraction (at room and high temperature), differential thermal analysis, thermogravimetry and scanning electron microscopy. The results confirm the formation of the solid solution in the whole range of composition. The influence of Li addition on the dielectric permittivity and losses and on the ferro-paraelectric transition temperature is also studied.  相似文献   

13.
Large-scale single crystalline vanadium oxide nanobelts were synthesized by hydrothermal treatment of NH4VO3 in the presence of polymer PEG-4000 at 180 °C for 24 h. Techniques of SEM, TEM, XRD, FT-IR, HRTEM, and SAED were used to characterize the morphology, composition and structure of the as-obtained nanobelts. The as-prepared vanadium oxide nanobelts are up to several hundreds micrometers in length, 100 nm–1 μm in width, 20–30 nm in thickness, and grow along the [1 0 0] direction. PEG plays a critical role for the formation of the vanadium oxide nanobelts in the present synthetic system. A preliminary formation mechanism was proposed to account for the formation of the as-obtained nanobelts.  相似文献   

14.
100-nm thick films of Al1 ? xCux alloys were prepared on glass substrates by thermal diffusion technique. The Cu atomic concentration was varied from 10% to 90%. Alloys were prepared at different temperatures into a vacuum oven with Argon atmosphere. Two thermal processes were used: i) heating the film at 400 °C in a single step, and ii) heating the films in sequential steps at 100, 200, 300 and 400 °C. Morphology, electrical resistivity, and crystalline orientation of the alloys were studied. The electrical resistivity and surface roughness of the alloys were found to depend strongly on the atomic composition and the diffusion temperature. However, we did not find differences between samples prepared under the two thermal processes. Alloys prepared with x = 0.6 and x = 0.1–0.3 as Cu at concentration exhibited values on electrical resistivity and surface roughness lower than pure Al. Different phases of the Al1 ? xCux films were observed as a function of Cu concentration showing a good agreement with the AlCu phase diagram.  相似文献   

15.
Effects of 1.0 wt.% V2O5–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO4 ceramics have been investigated. BiSbO4 ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V2O5–CuO mixtures addition with different ratios of CuO to V2O5. The formation of BiVO4 phase and substitution of Cu2+ can explain the decrease of sintering temperature. Dense BiSbO4 ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C?1 and ?77.8 ppm °C?1. BiSbO4 ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.  相似文献   

16.
In the present work, the 0.3Li2TiO3–0.7Li(Zn0.5Ti1.5)O4 ceramic was prepared via the conventional solid state reaction route, and the phase composition, microstructure, and sintering behavior were investigated. The ceramic sample sintered at 1100 °C for 2 h demonstrated high microwave dielectric performance with a relative permittivity of 23.5, a high quality factor (Qf) ~ 88,360 GHz (at 7.4 GHz), and near zero temperature coefficient of resonant frequency about ? 0.8 ppm/°C. These results indicate that the 0.3Li2TiO3–0.7Li(Zn0.5Ti1.5)O4 ceramic might be a good candidate for dielectric resonators, filters and other microwave electronic device applications.  相似文献   

17.
Biaxially textured CeO2-based oxide films with crack-free and smooth surface were prepared by metal-organic deposition (MOD) on Ni-W alloy tapes after annealing. In this study, addition of B2O3-based precursors to precursor solution and their effects on crystallinity and surface roughness of the CeO2-based oxide films were investigated. As the amount of added B2O3-based precursors increased, the relative intensity of CeO2 (200) peak was monotonously increased and much smoother surface was obtained. Microcracks in CeO2 films were successfully suppressed by substituting gadolinium for part of cerium in the CeO2 films. In addition to this, a biaxially textured Ce0.75Gd0.25O2-4.5% B2O3 film (Δθ = 4.8°, Δ? = 7.4°) with smooth surface (Rq = 2.7 nm) was successfully grown on the Ni-W tape after annealing at 900 °C.  相似文献   

18.
《Materials Research Bulletin》2006,41(6):1063-1068
Cerium oxide (CeO2) buffer layers play an important role for the development of YBa2Cu3O7−x (YBCO) based superconducting tapes using the rolling assisted biaxially textured substrates (RABiTS) approach. The chemical solution deposition (CSD) approach has been used to grow epitaxial CeO2 films on textured Ni–3 at.% W alloy substrates with various starting precursors of ceria. Precursors such as cerium acetate, cerium acetylacetonate, cerium 2-ethylhexanoate, cerium nitrate, and cerium trifluoroacetate were prepared in suitable solvents. The optimum growth conditions for these cerium precursors were Ar–4% H2 gas processing atmosphere, solution concentration levels of 0.2–0.5 M, a dwell time of 15 min, and a process temperature range of 1050–1150 °C. X-ray diffraction, AFM, SEM, and optical microscopy were used to characterize the CeO2 films. Highly textured CeO2 layers were obtained on Ni–W substrates with both cerium acetate and cerium acetylacetonate as starting precursors. YBCO films with a Jc of 1.5 MA/cm2 were obtained on cerium acetylacetonate-based CeO2 films with sputtered YSZ and CeO2 cap layers.  相似文献   

19.
《Materials Research Bulletin》2013,48(4):1587-1592
Nanocrystalline spinel NiFe2O4 was synthesized by a novel low temperature route. The crystal structure, composition and morphology of the as-prepared powder were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The average diameter of the particles prepared at 700 °C is about 30 nm. The electrochemical reaction mechanism and charge–discharge mechanism of the nanocrystalline NiFe2O4 were proposed based on thermogravimetric analysis (TGA) and cyclic voltammogram study. The charge–discharge tests indicated that the sample calcined at 700 °C shows the highest initial discharge capacity (1400 mAh g−1) attributed to the nanometer size and the better crystallinity of the powder. A discharge capacity stabilizes at about 600 mAh g−1 after 10 cycles. The columbic efficiency is improved. The synthesis method is relatively low cost and convenient for large-scale production.  相似文献   

20.
Lead-free ferroelectric (K, Na)NbO3 (KNN) thin films (~200 nm thickness) were prepared using a modified sol–gel method by mixing K and Na acetates with the Nb–tartarate complex, deposited by spin-coating method on Pt/Al2O3 and Pt/SiO2/Si substrates and sintered at 650 °C. Pure perovskite phase of K0.65Na0.35NbO3 in film on silicon were revealed, while film on alumina contained also small amount of secondary pyrochlore Na2Nb8O21 phase. Homogenous microstructure of film on Si substrate was smoother with the lower roughness (~7.4 nm) and contained spherical (~50 nm) particles. The mechanical properties of films were characterized by nanoindentation. The modulus and hardness of KNN films were calculated from their composite values of film/substrate systems using discontinuous and modified Bhattacharya model, respectively. The KNN film modulus was higher on alumina substrate (91 GPa) in comparison with silicon substrate (71 GPa) and values of film hardness were the same (4.5 GPa) on both substrates.  相似文献   

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