Oxalate Precursor Route Research Articles

Structural, thermal and dielectric behavior of Polyaryletherketone (PAEK)/CaCu3Ti4O12 (CCTO) nanocomposite films

Polyaryletherketone (PAEK)/CaCu3Ti4O12 (CCTO) nanocomposite films with various (0, 1, 5, 10 and 20) weight % CCTO were fabricated via melt-compounding followed by film extrusion process. CCTO nanoceramics (nCCTO) with a crystallite size of about 30–100 nm were prepared from oxalate precursor route. Thickness of the fabricated films was in the range of 50–80 μm, and these films were characterized for their structural, thermal, and dielectric behavior. X-ray diffraction analyses showed the presence of peaks corresponding to both PAEK and CCTO with varying intensities. Fourier transform infrared (FTIR) studies revealed that the chemical structure of PAEK was unaltered by the incorporation of nCCTO. Melting temperature of pure PAEK was about 372 °C, which did not change significantly with the addition of nCCTO. Thermo-gravimetric analysis was carried out to study the thermal stability of these nanocomposites. Frequency independent dielectric behavior was observed in case of all nanocomposite films. Room temperature dielectric permittivity of PAEK (3.3 at 10 kHz) was enhanced with the addition of nCCTO, and for 20 wt% loading a value of 4.5 was achieved. Low values of dielectric loss (0.005–0.009) were obtained for all nanocomposite films at 10 kHz. These nanocomposites can be explored as possible dielectric materials for capacitor applications.

CaCu3Ti4O12: A Bifunctional Perovskite Electrocatalyst for Oxygen Evolution and Reduction Reaction in Alkaline Medium

Perovskite oxides are prominent materials as the bifunctional electrocatalysts for both oxygen reduction/evolution reactions (ORR/OER) for the electrochemical energy conversion and storage using regenerative fuel cells and rechargeable metal-air batteries. In this work, a quadruple perovskite CaCu3Ti4O12 has been synthesized oxalate precursor route. X-ray diffraction pattern shows phase purity of the synthesized electrocatalyst. The synthesized CCTO electrocatalyst have crystallite size of 26nm. Electrochemical investigations reveal that CCTO exhibit efficient catalytic activity. More interestingly, an extremely high OER activity is observed for CCTO electrocatalysts which is found superior than similar class of perovskites. Additionally, CCTO shows efficient ORR activity with an onset potential of 0.83V which is better than that of Pt/C catalyst (≈0.94V). These results demonstrate the significant potential of CCTO perovskite as a bifunctional electrode material for alkaline fuel cells and metal-air batteries.

Bi2(C2O4)3·7H2O and Bi(C2O4)OH Oxalates Thermal Decomposition Revisited. Formation of Nanoparticles with a Lower Melting Point than Bulk Bismuth.

Two bismuth oxalates, namely, Bi2(C2O4)3·7H2O and Bi(C2O4)OH, were studied in terms of synthesis, structural characterization, particle morphology, and thermal behavior under several atmospheres. The oxalate powders were produced by chemical precipitation from bismuth nitrate and oxalic acid solutions under controlled pH, then characterized by X-ray diffraction (XRD), temperature-dependent XRD, IR spectroscopy, scanning electron microscopy, and thermogravimetric differential thermal analyses. New results on the thermal decomposition of bismuth oxalates under inert or reducing atmospheres are provided. On heating in nitrogen, both studied compounds decompose into small bismuth particles. Thermal properties of the metallic products were investigated. The Bi(C2O4)OH decomposition leads to a Bi-Bi2O3 metal-oxide composite product in which bismuth is confined in a nanometric size, due to surface oxidation. The melting point of such bismuth particles is strongly related to their crystallite size. The nanometric bismuth melting has thus been evidenced ∼40 °C lower than for bulk bismuth. These results should contribute to the development of the oxalate precursor route for low-temperature soldering applications.

Tunable optical properties of some rare earth elements-doped mayenite Ca12Al14O33 nanopowders elaborated by oxalate precursor route

Rare earth (RE) ions-doped mayenite Ca12Al14−xRExO33 nanopowders (where RE = La and Gd and x = 0–1.0) were synthesized using the oxalate precursor technique. The as-prepared precursors were calcined at 800 °C for 2 h. Obviously, all RE-doped Ca12Al14−xRExO33 possessed a well-crystalline cubic mayenite phase till RE content of 0.8. The crystallo-chemical aspects including crystallite size, lattice parameters, theoretical X-ray density and bulk density were robustly on RE nature and ratio. The microstructure and the average grain size were significantly influenced by the RE kind and content. The high transparency of Ca12Al14−xRExO33 over 80% was found to be evinced in the visible wavelength range of 400–800 nm. Besides, the incorporation of RE cation minimized the direct band gap energy from 4.42 eV for pure mayenite to 3.85 and 3.59 eV with x value 1.0 of La3+ and Gd3+ ions. The photoluminescence spectra of pure mayenite nanoparticles showed that the band edge emission (λexc = 248 nm) with an intense visible emission band at 360 nm was detected. Otherwise, the band edge emission showed a slight shift toward short wavelength due to the substitution Al3+ by RE3+ ions. Such results open a new avenue for application of mayenite as a good candidate for transparent low-temperature electron conductor for optoelectronics applications.

Studies on the structural, thermal, and dielectric properties of fabricated Nylon 6,9/CaCu3Ti4O12 nanocomposites

AbstractNylon 6,9/CaCu3Ti4O12 (CCTO) nanocrystal composites with relatively high dielectric permittivity (220 at 100 Hz) were fabricated by melt mixing followed by hot pressing. The CCTO nanoceramics were synthesized using the oxalate precursor route, and the transmission electron microscopy studies exhibited that the crystallites are in the range of 20–200 nm. The nanocomposites were characterized using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and impedance analyzer to study their structural, thermal, and dielectric properties. The introduction of CCTO nanoparticles into the matrix had influenced the thermal properties. The effective dielectric permittivity of the nanocomposite increased by the augmentation of CCTO content in the Nylon 6,9. Our experimental outcomes showed that the fixed dielectric permittivity of such two-phase composite was established above 200 when the CCTO concentration was closer to its percolation threshold. The room temperature dielectric permittivity as high as 220 at 100 Hz has been achieved when the CCTO content increased to 58 vol% in the polymer and this was increased to 3845 at 150°C. The increase in AC conductivity with the increase in the CCTO content in the polymer matrix supported the hopping of the charge carrier conduction mechanism.

A comparative study on dielectric, structure, and thermal behavior of micro‐ and nano‐sized CCTO in nylon 6,9 matrix

Calcium copper titanium oxalate CaCu3Ti4O12 (CCTO) particles as a filler with both micro‐ and nano‐sized into nylon 6,9 polymer have been investigated under structural, thermal, and dielectric properties to find that particle satisfy all the same. Micro‐sized CCTO particles (point out as mCCTO) was synthesized using solid‐state route using ball milling and nano‐sized CCTO particles (point out as nCCTO) was synthesized using complex oxalate precursor route. Fabrication of nylon 6,9/CCTO composite for both micro‐ and nano‐sized CCTO particles were employed separately into nylon 6,9 matrix and examined comparatively. The composite containing 20 vol% of nCCTO achieve 24.5 dielectric permittivity at 100 Hz in room temperature that was significantly higher than mCCTO which was 14 at the same condition. From the structural analysis, we obtained that the nCCTO was well dispersed in the matrix medium, whereas the mCCTO were also dispersed with some agglomeration that was the reason for the interaction failure between the particles and matrix material. The dielectric permittivity results obtained from this study specify that the composite containing nano‐sized CCTO particles may be suitable for energy storage devices and in the higher temperature sensor applications. POLYM. COMPOS., 38:927–935, 2017. © 2015 Society of Plastics Engineers

Structural characterization and properties of nanocrystalline Sn1−xCoxO2 based dilute magnetic semiconductors

Abstract

Piezoelectric properties of individual nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 obtained by oxalate precursor route

Ferroelectric domain pattern and piezoresponse (d33) versus DC bias voltage for the BCZT nanocrystalline powder.

Tuning the optical, electrical and magnetic properties of Ba(0.5)Sr(0.5)Ti(x)M(1-x)O3 (BST) nanopowders.

Metal doped barium strontium titanate (BST; Ba0.5Sr0.5TixM1-xO3) nanopowders have been successfully synthesized through the oxalate precursor route based on low cost starting materials. The effect of metal ion substitution, namely Fe(3+), Mn(2+), Co(2+) and Y(3+), on the crystal structure, microstructure and optical, electrical, dielectric and magnetic properties of BST was studied. The results revealed that a crystalline single cubic BST phase was formed for pure and Mn(2+), Co(2+) and Y(3+) ion-substituted BST samples, whereas a tetragonal BST structure was obtained for the Fe(3+) substituted BST sample at an annealing temperature of 1000 °C for 2 h. Furthermore, addition of the metal ions was found to decrease the crystallite size and unit cell volume of the produced BST phase. The microstructure of the produced pure BST phase was metal ion dependent. Most BST particles appeared as a cubic like structure. The transparency of BST was found to increase with metal substitution. Meanwhile, the band gap energy was increased from 3.4 eV for pure BST to 3.8, 4.1, 4.2 and 4.3 eV as the result of substitution by Fe(3+), Mn(2+) and Co(2+) and Y(3+) ions, respectively. The DC resistivity was metal ion dependent. The highest DC resistivity (ρ = 66.60 × 10(5) Ω cm) was accomplished with the Mn(2+) ion. Moreover, the addition of metal ions decreased the dielectric properties of the expected Mn(2+) ion and increased the magnetic properties.

Grain and the concomitant ferroelectric domain size dependent physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics fabricated using powders derived from oxalate precursor route

Fine powders comprising nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) were synthesized via oxalate precursor method, which facilitated to obtain homogenous and large grain sized ceramics at a lower sintering temperature. The compacted powders were sintered at various temperatures in the range of 1200 °C–1500 °C for an optimized duration of 10 h. Interestingly the one that was sintered at 1450 °C/10 h exhibited well resolved Morphotrophic Phase Boundary. The average grain size associated with this sample was 30 μm accompanied by higher domain density mostly with 90° twinning. These were believed to have significant contribution towards obtaining large strain of about 0.2% and piezoelectric coefficient as high as 563 pC/N. The maximum force that was generated by BCZT ceramic (having 30 μm grain size) was found to be 161 MPa, which is much higher than that of known actuator materials such as PZT (40 MPa) and NKN-5-LT (7 MPa).

Optical and magnetic properties of Sn1−xMnxO2 dilute magnetic semiconductor nanoparticles

Sn1−xMnxO2 (x=0.05, 0.10 and 0.15) nanoparticles with tetragonal structure have been successfully synthesized by solvothermal method using oxalate precursor route. The oxalate precursors and its corresponding oxides were characterized by powder X-ray diffraction (PXRD), thermogravimetric (TG), fourier transform infrared (FTIR) and transmission electron microscopic (TEM) studies. PXRD studies showed the highly crystalline and monophasic nature of the solid solutions. The shifting of X-ray reflections towards higher angle is attributed to the incorporation of Mn2+ ions in SnO2 host lattice. The average particle size was found to be in the range of 5–11nm. Reflectance measurements showed blue shift in energy band gap which increases with increasing Mn2+ concentration. Surface area of these nanoparticles (59–388m2/g) was found to be high which increases with increasing the dopant ion concentration. Mn-doped SnO2 showed distinct magnetic behaviour with different manganese concentration. Sn1−xMnxO2 (x=0.05 and 0.10) revealed the parasitic ferromagnetism, however on increasing x=0.15, sample showed paramagnetic behaviour.

Oxalate precursor preparation of Li1.2Ni0.13Co0.13Mn0.54O2 for lithium ion battery positive electrode

Li1.2Ni0.13Co0.13Mn0.54O2 powders have been prepared through co-precipitation of metal oxalate precursor and subsequent solid state reaction with lithium carbonate. X-ray diffraction pattern shows that the massive rock-like structure has a good layered structure and solid solution characteristic. Scanning electron microscope and transition electron microscope images reveal that the Li1.2Ni0.13Co0.13Mn0.54O2 composed of nanoparticles have the size of 1–2 μm. As a lithium ion battery positive electrode, the Li1.2Ni0.13Co0.13Mn0.54O2 has an initial discharge capacity of 285.2 mAh g−1 at 0.1 C within 2.0–4.8 V. When the cutoff voltage is decreased to 4.6 V, the cycling stability of product can be greatly improved, and a discharge capacity of 178.5 mAh g−1 could be retained at 0.5 C after 100 cycles. At a high charge–discharge rate of 5 C (1,000 mAh g−1), a stable discharge capacity of 121.4 mAh g−1 also can be reached. As the experimental results, the Li1.2Ni0.13Co0.13Mn0.54O2 prepared from oxalate precursor route is suitable as lithium ion battery positive electrode.

Optical, magnetic and structural characterization of Zn1 − x Co x O nanoparticles synthesized by solvothermal method

Nanoparticles of Co-doped ZnO with 3·8, 7·2 and 11·5 wt% were synthesized by solvothermal method through oxalate precursor route. X-ray diffraction studies showed the formation of hexagonal ZnO structure for x = 0·038, however, secondary phase of Co3O4 arises on increasing the Co content up to 11·5%. Transmission electron microscopic studies showed that particles are in the nano-metric regime and the grain size decreases on increasing the Co concentration. Optical reflectance measurements showed an energy bandgap, which decreases on increasing Co concentration. Specific surface area of these nanoparticles was found to be very high and comes out to be 97·6, 112·1 and 603·8 m2g − 1, respectively. All the solid solutions showed paramagnetism with weak antiferromagnetic interactions. It is seen that the antiferromagnetic interaction increases on increasing Co concentration.

Structural characterization and properties of nano-sized Cd1−xCoxO dilute magnetic semiconductors prepared by solvothermal method

Nanoparticles of Co-doped CdO with 4.2, 9.3, and 15.4 weight% were successfully synthesized by a modified solvothermal method through oxalate precursor route. The oxalate served as an excellent precursor for the synthesis of pure and homogeneous oxide nanoparticles. Powder X-ray diffraction studies revealed the monophasic nature of these nanoparticles. The lattice parameter decreased monotonically with increasing Co concentration, confirming Co was doped into the CdO host lattice. Particle size decreased and surface area increased on increasing the dopant ion concentration. Optical absorption measurements showed an energy band gap that increased with Co concentration. Magnetization studies indicated that the samples showed paramagnetic behavior with weak antiferromagnetic interactions.

Effect of TeO2 addition on the dielectric properties of CaCu3Ti4O12 ceramics derived from the oxalate precursor route

CaCu 3 Ti 4 O 12 (CCTO) ceramics which has perovskite structure gained considerable attention due to its giant permittivity. But it has high tan δ (0.1 at 1 kHz) at room temperature, which needs to be minimized to the level of practical applications. Hence, TeO 2 which is a good glass former has been deliberately added to CCTO nanoceramic (derived from the oxalate precursor route) to explore the possibility of reducing the dielectric loss while maintaining the high permittivity. The structural, morphological and dielectric properties of the pure CCTO and TeO 2 added ceramics were studied using X-ray diffraction, Scanning Electron Microscope along with Energy Dispersive X-ray Analysis (EDX), spectroscopy and Impedance analyzer. For the 2.0 wt.% TeO 2 added ceramics, there is a remarkable difference in the microstructural features as compared to that of pure CCTO ceramics. This sample exhibited permittivity values as high as 7387 at 10 KHz and low dielectric loss value of 0.037 at 10 kHz, which can be exploited for the high frequency capacitors application.

Solvothermal synthesis of Zn1−xMnxO nanoparticles using oxalate precursor route: Optical and magnetic properties

Nanoparticles of Zn1−xMnxO (x=0.022, 0.061 and 0.098) were synthesized by a modified solvothermal method through the oxalate precursor route. The precursors were characterized by TG/DTA analysis. Their kinetics has also been studied using the Freeman and Carroll method. The prepared oxide nanoparticles were investigated by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), optical and BET surface area studies. PXRD patterns were matched with hexagonal ZnO structure, however few impurity peaks of ZnMnO3 appeared. Reflectance measurements showed that Mn2+ is incorporated in the Zn matrix. The band gap decreases on increasing Mn concentration. The particle size decreases from 18 to 9nm and the surface area increases (255.4–582.9m2g−1) on increasing Mn concentration. All these solid solutions show paramagnetic behaviour with very weak antiferromagnetic interactions. The effective magnetic moment of these nanoparticles comes out to be 4.91, 4.77 and 4.18 μB/Mn2+.

Optical and electrical properties of Ba1−x Sr x TiO3 nanopowders at different Sr2+ ion content

Barium strontium titanate (BST) Ba1−x Sr x TiO3 nanopowders have been successfully synthesized using oxalate precursor route. The effect of Sr2+ ion content from 0.3 to 0.7 on the crystal structure, crystallite size, microstructure, electrical and optical properties was systematically studied. The results revealed that well crystalline single BST phase was formed by annealing the oxalate precursor at 1,000 °C for 2 h. The crystallite size of the BST powders was decreased with increasing the Sr2+ ion molar ratios. The crystallite size was decreased from 56.0 to 33.1 nm when the Sr2+ ion content increased from 0.3 to 0.7. Additionally, the lattice parameter (a), unit cell volume and X-ray density of BST ware decreased whereas the porosity, % were increased with Sr2+ ion concentration. The BST phase appeared as cubic-like structure. The spectrophotometer measurement results demonstrated that the room temperature band gap energy varied with the Sr2+ ion composition x. The band gap energy was shifted to low energy and it was decreased from 3.6 to 3.2 eV with increasing the Sr2+ ion content from 0.3 to 0.7. Moreover, the DC resistivity was enhanced with increasing the Sr2+ ion ratio. The dielectric response obtained for the stressed samples corresponds to a true resonance rather than a dispersion process with a characteristic frequency around 1 GHz at room temperature. However, the peaks commonly observed at GHz frequency were changed with varying the Sr2+ ion composition. The high imaginary components of dielectric permittivity for x = 0.3 was found at higher frequency region around 1.6 GHz compared with the samples with x values of 0.5 and 0.7 in which the frequency regions were around 1.25 and 1.15 GHz, respectively.

Solvothermal Synthesis of In2−xCoxO3 (0.05 ≤ x ≤ 0.15) Dilute Magnetic Semiconductors: Optical, Magnetic, and Dielectric Properties

Highly crystalline and monophasic nanoparticles of In2−xCoxO3 (0.05 ≤ x ≤ 0.15) were successfully synthesized by the solvothermal method through an oxalate precursor route. Collective evidence from X‐ray diffraction and reflectance measurements suggest that the Co2+ is incorporated into the In2O3 lattice site. Effect of cobalt dopant on the growth and morphology of indium oxide was studied by transmission electron microscopy. It has been observed that particle size decreases from 23 to 9 nm on increasing the Co concentration. High surface area has been obtained, with values ranging between 66 and 151 m2/g, respectively. Values for the dielectric constant were around 40. All these solid solutions show paramagnetic behavior with weak antiferromagnetic interactions.

Effect of γ-rays irradiation on Mn–Ni ferrites: Structure, magnetic properties and positron annihilation studies

Manganese–nickel ferrites powder with general formula MnxNi1−xFe2O4 (x=0.0, 0.2, 0.4) were synthesized through oxalate precursor route and sintered at 1000°C. The X-ray diffraction (XRD) patterns were measured for the prepared samples to confirm the existence of single-phase structure. The crystallite size was estimated and found to be within the range 125–170nm. To study the radiation effect on the structure and magnetic properties, a representative group of the investigated samples were irradiated by γ-rays of 60Co source with a dose of 310kGy. The XRD spectra were performed for the irradiated samples and compared with that of the pristine samples to estimate changes in the structure. The obtained results showed that the crystallite size increased by a factor of 10–16% after gamma irradiation. The lattice parameter also was increased due to the conversion of Fe3+ (0.64Å) to Fe2+ (0.76Å). The formula of the cation distribution of the ferrites samples was suggested at x=0, 0.2, 0.4 before and after irradiation. The theoretical lattice parameter, sample density and porosity were calculated and compared with that obtained from the experimental data. Good agreement was found between theoretical and experimental structural data which confirms the proposed formula of cations distribution. The hysteresis curves were measured using vibrating sample magnetometer (VSM) for the unirradiated and irradiated samples and the saturation magnetization was estimated. The obtained results showed increase in saturation magnetizations (Ms) for all the samples by irradiation due to redistribution of the cations between A and B sites and changing the net magnetic moments. Theoretical calculation of magnetic moments and saturation magnetization using the proposed cations distribution of A and B sites confirmed the experimental results. The positron annihilation lifetime spectroscopy (PALS) was used to investigate the defects and changes in electron density after irradiation. The PAL parameters (τ1, I1, τ2, I2 and mean lifetime) show that the irradiation affects the size and concentration of the vacant type defects. The results reveal that there are some large voids (with radius ranged from 0.28 to 0.38nm and mean value of 0.34±0.04nm in the studied samples). The obtained results indicate the high sensitivity of PALS technique to the enhanced structure changes due to gamma rays irradiation.

Optical and magnetic properties of CuO/CuFe2O4 nanocomposites

CuO/c-CuFe2O4 nanocomposites have been synthesized via the oxalate precursor route. Effect of synthesis conditions on the crystal structure, microstructure, magnetic and optical properties of the formed powders was studied. The results indicated that pure CuO nanoparticles were obtained from the oxalate precursor annealed at 600 °C for 2 h. However, substitution of Cu2+ ion by Fe3+ ion (Cu1−X Fe X O, where X = 0, 0.05, 0.1 and 0.2) led to form of CuO/CuFe2O4 nanocomposites. The microstructures of the powders appeared as a monoclinic like shape. Furthermore, the band gap energy of the obtained CuO nanopowders was 1.41 eV and the value was slightly decreased by Fe3+ ion substitution. In addition, the formed CuO particles had weak ferromagnetic characteristics. However, the substitution Cu2+ ion by Fe3+ ion enhanced the magnetic properties of the formed composite as the result of increasing the CuFe2O4 phase formation. Hence, the saturation magnetization was increased from 0.13 to 9.8 emu/g by increasing the Fe3+ ion from 0 to 0.2.