W. Zhu

Preparation and characterization of Pb(Zr0.52Ti0.48)O3 ceramics from high-energy ball milling powders

Abstract Ultra-fine Pb(Zr0.52Ti0.48)O3 powder has been synthesized from the commercial PbO, TiO2 and ZrO2 powders using the high-energy ball milling technique in air at room temperature without any post-annealing. The synthesized powders milling for different hours are characterized using XRD, SEM, TEM and Raman spectra. XRD patterns and Raman spectra show that the perovskite phase of PZT can be formed from the mixture of the starting materials after milling for 20 h. The grain sizes of the powders have been estimated from the XRD patterns and TEM images to be ∼10 nm. The relationship between the microstructure of the PZT powders and the milling hours has been discussed. The PZT ceramics are derived for the synthesized powders by sintering the green pellets at 1100°C for 1 h. The dielectric properties of the PZT samples are comparable with those of the same composition PZT prepared by other methods, but the high-energy ball milling process is much easier than other reported methods. The high-energy ball milling method offers a very attractive advantage of avoiding the loss of volatile elements, such as Pb, Bi, in the procedure of synthesis of nano-powders with their uniform compositions.

Ethanol sensors based on nano-sized α-Fe2O3 with SnO2, ZrO2, TiO2 solid solutions

Abstract Nano-sized α-Fe 2 O 3 based solid solutions with different compositions of SnO 2 , ZrO 2 and TiO 2 , were prepared using high-energy ball milling technique. Their structural properties and ethanol gas sensing properties were characterized using XRD and gas sensing measurements. The experimental results show that the mechanical alloying processes for these powders are the same. The screen-printed thick film gas sensors made from these mechanically alloyed materials demonstrated very high relative resistance. A non-equilibrium structural model was proposed to explain sensing mechanism. The comparison of gas sensing properties was performed for different α-Fe 2 O 3 based solid solutions with optimized compositions of SnO 2 , ZrO 2 and TiO 2 . Among these three sensors, x TiO 2 –(1− x )α-Fe 2 O 3 type of gas sensor has much lower relative resistance value for ethanol. This can be elucidated by the different valence states exhibited by titanium ions.

Size effect and gas sensing characteristics of nanocrystalline xSnO2-(1−x)α-Fe2O3 ethanol sensors

Abstract Non-equilibrium nanocrystalline x SnO 2 -(1− x )α-Fe 2 O 3 powders have been prepared using the mechanical alloying technique. The thick film screen printing technology is then employed to fabricate these ethanol gas sensors. Their particle size and structural properties are systematically characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The gas sensing characteristics are also measured. Based on the experimental results, we have observed that particle size of the powders is drastically milled down to about 10 nm after 24 h of high-energy milling. A very high gas sensitivity value of 845 for 1000 ppm of ethanol gas in air has been obtained. Our proposed new structural model for these non-equilibrium nanocrystalline x SnO 2 -(1− x )α-Fe 2 O 3 materials explains both the lattice expansion of these high energy mechanically alloyed powders as well as the charge neutrality in terms of additional oxygen dangling bonds at the nano-sized particle surfaces. It is those enormous oxygen-dangling bonds at the particle surfaces that give rise to the high gas sensitivity. The sensors are found to be 32.5 times more selective to the ethanol gas compared to CO and H 2 gases.

Preparation of Bi4Ti3O12 ceramics via a high-energy ball milling process

Abstract Nano-sized bismuth titanate (Bi4Ti3O12) powders were prepared by a high-energy ball milling process directly from their oxide mixture of Bi2O3 and TiO2. Bi4Ti3O12 phase can be formed from the oxide mixture after milling for 9 h. Almost single phase of Bi4Ti3O12 is obtained after milling for 15 h. With increasing milling time, the particle size of the mixture is gradually reduced. Bi4Ti3O12 ceramics were obtained by sintering the synthesized powders at temperatures ranging from 750°C to 950°C. The Bi4Ti3O12 ceramics sintered at 850°C for 1 h exhibited a density of 7.91 g/cm3, a dielectric of 243 and a dielectric loss of 0.017, and a remnant polarization of 24 μC/cm2 and a coercive field of 11 kV/cm, respectively. Piezoelectric parameters of the Bi4Ti3O12 ceramics are k33=56%, k31=58%. The Bi4Ti3O12 ceramics also possessed good pyroelectric properties. These results indicate that high-energy ball milling process is a promising way to prepare Bi4Ti3O12 ceramics.

Frequency and temperature dependent impedance spectroscopy of cobalt ferrite composite thick films

Cobalt ferrite (CoFe2O4) composite thick films consisting of two different sized CoFe2O4 particles were deposited on Pt/Ti/SiO2/Si substrate by a hybridized sol-gel processing and spin coating technique. X-ray diffraction analysis showed a pure spinel phase of CoFe2O4, which was also confirmed by micro-Raman spectra. Scanning electronic microscope indicated a dense microstructure with a thickness above 8u2002μm. The detailed electrical investigations were conducted in the frequency range of 100 Hz–1 MHz and temperature range between 25 and 200u2009°C. Real and imaginary parts of impedance (Z′ and Z″) in the above frequency and temperature domain suggested the coexistence of two relaxation regimes: one was induced by electrode polarization; while the other was attributed to the coeffect of grains and grain boundaries, which was totally different from its counterpart of bulks and also not reported in other ferrites. Electrical modulus (M′ and M″) further showed the crossover from grains effect to grain boundaries e...

Preparation of Fe2O3(0.9)–SnO2(0.1) by hydrazine method: application as an alcohol sensor

Abstract Nanocrystalline Fe 2 O 3(0.9) –SnO 2(0.1) powders have been prepared using a hydrazine method by adding hydrazine monohydrate to an aqueous solution of ferric nitrate nanohydrate, (Fe(NO 3 ) 3 ·9H 2 O) and tin tetra chloride (SnCl 4 ), followed by washing and drying. This material has been characterized by different techniques such as gravimetric-differential thermal analysis (TGA/DTA), X-ray diffraction (XRD). Sensors made from this material have been proved to be highly sensitive and selective in the detection of ethanol. The sensitivity for ethanol has been compared with a 10xa0wt.% of ZrO 2 and SnO 2 loaded in Fe 2 O 3 . The ethanol sensitivity of pure and Pt doped Fe 2 O 3(0.9) –SnO 2(0.1) and Fe 2 O 3(0.9) –ZrO 2(0.1) has been investigated for its electrical resistance. The high sensitivity of the sensor to the ethanol could be explained on the basis of a SnO 2 , ZrO 2 activity that invokes the acid–base properties of sensing materials towards the sensitive detection of ethanol vapor in air. Its cross-sensitivity to other gases like CH 4 , CO, and H 2 has also been carried out.

Microstructure, dielectric properties and hydrogen gas sensitivity of sputtered amorphous Ba0.67Sr0.33TiO3 thin films

Abstract A novel metal-ferroelectric hydrogen gas sensing device was fabricated on platinum-coated silicon wafer with an amorphous ferroelectric Ba0.67Sr0.33TiO3 layer using the RF magnetron co-sputtering process and was characterized by X-ray diffraction, transmission electron microscopy, dielectric characterization and gas sensing measurement. Experimental results show that the microstructure and the dielectric properties are closely correlated with the deposition parameters. The studies on the dielectric properties indicate that the non-stoichiometric defects in the amorphous films are largely reduced by depositing in 50% oxygen content just below the crystallization temperature of the films. J–E performances exhibit the typical Schottky behavior, both in air and in hydrogen gas and a voltage shift 0.6 V has been observed in 1042 ppm hydrogen diluted in air. Compared to the sol-gel case, it is believed that the electronic defects, both in bulk and at interface, cause the degradation of the hydrogen gas sensitivity and weaken the induced H2 potential built-up across the space charge layer at the interface. The gas sensing mechanism based on the proton induced Pd/BST interfacial polarization potential is also discussed. Related to the MIS hydrogen sensor device, it is believed that the high permittivity of the amorphous ferroelectric thin films enhances the proton polarization at the Pd/BST interface and, in turn, greatly improves the built-up interfacial potential induced by the hydrogen.

Structural and gas sensing properties of ultrafine Fe2O3 prepared by plasma enhanced chemical vapor deposition

Abstract Ultrafine Fe2O3 powders have been obtained using the plasma enhanced chemical vapor deposition (PECVD) method for the gas sensor application. Ferrocene is used as the precursor source in the PECVD powder preparation procedure. The structural properties of these ultrafine Fe2O3 powders have been systematically characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and thermogravimetric analysis (TGA). DTA results show that the oxygen-rich atmosphere is more favorable than nitrogen for the burn-off of residual organic compounds in the precursor powders. It is interesting to note from TEM and X-ray diffraction patterns that β- and γ-Fe2O3 phases can co-exist with the α-Fe2O3 phase due to the size effect, depending upon processing conditions. The activation energy as a function of temperature and grain size is estimated. It is found that at lower temperatures, the activation energy for crystallization predominates; while at higher temperatures, the larger activation energy is attributed to the grain growth process. The gas sensitivities and dynamic conductance measurement for these ultrafine Fe2O3 gas sensors have also been investigated.

Facile room-temperature synthesis of carboxylated graphene oxide-copper sulfide nanocomposite with high photodegradation and disinfection activities under solar light irradiation

Carboxylic acid functionalized graphene oxide-copper (II) sulfide nanoparticle composite (GO-COOH-CuS) was prepared from carboxylated graphene oxide and copper precursor in dimethyl sulfoxide (DMSO) by a facile synthesis process at room temperature. The high-effective combination, the interaction between GO-COOH sheets and CuS nanoparticles, and the enhanced visible light absorption were confirmed by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS) and Photoluminescence (PL) spectra. The as-synthesized GO-COOH-CuS nanocomposite exhibited excellent photocatalytic degradation performance of phenol and rhodamine B, high antibacterial activity toward E. coli and B. subtilis, and good recovery and reusability. The influence of CuS content, the synergistic reaction between CuS and GO-COOH, and the charge-transfer mechanism were systematically investigated. The facile and low-energy synthesis process combined with the excellent degradation and antibacterial performance signify that the GO-COOH-CuS has a great potential for water treatment application.

Microstructure and hydrogen gas sensitivity of amorphous (Ba,Sr)TiO3 thin film sensors

Abstract Ferroelectric (Ba0.67Sr0.33)Ti1.02O3 thin films have been prepared by the sol–gel technology and characterized using TGA, DTA, XRD, TEM, dielectric characterizations, and gas sensing properties. The (Ba0.67Sr0.33)Ti1.02O3 thin film devices are made on Pt-coated Si substrate to detect hydrogen gas and to study gas sensing mechanism. Experimental results show that the diode I–V behavior appears in these Pd/amorphous (Ba,Sr)TiO3 (BST) thin film/metal capacitive devices, and that the enhanced voltage shift as large as 4.5 V at 1042 ppm hydrogen gas in air has been observed. Compared with the available data in the literature, this obtained value of voltage shift in our experiment is about seven times larger than the best one reported under similar testing conditions. It has been clearly shown that the hydrogen-induced voltage shift is closely correlated with the microstructure of ferroelectric thin films and the enhancement of this polarization potential is mainly attributed to the high dielectric constant of amorphous ferroelectric thin films. In this paper, we report our experimental results of this new hydrogen gas sensor and discuss the relationship between microstructure and hydrogen gas sensitivity in these ferroelectric thin film sensors.