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Typhoid fever is a public-health problem in Harare, the capital city of Zimbabwe, with seasonal outbreaks occurring annually since 2010. In 2019, the Ministry of Health and Child Care (MOHCC) organized the first typhoid conjugate vaccination campaign in Africa in response to a recurring typhoid outbreak in a large urban setting.As part of a larger public health response to a typhoid fever outbreak in Harare, Gavi approved in September 2018 a MOHCC request for 340,000 doses of recently prequalified Typbar-TCV to implement a mass vaccination campaign. To select areas for the campaign, typhoid fever surveillance data from January 2016 until June 2018 was reviewed. We collected and analyzed information from the MOHCC and its partners to describe the vaccination campaign planning, implementation, feasibility, administrative coverage and financial costs.The campaign was conducted in nine high-density suburbs of Harare over eight days in February-March 2019 and targeted all children aged 6 months-15 years; however, the target age range was extended up to 45 years in one suburb due to the past high attack rate among adults. A total of 318,698 people were vaccinated, resulting in overall administrative coverage of 85.4 percent. More than 750 community volunteers and personnel from the MOHCC and the Ministry of Education were trained and involved in social mobilization and vaccination activities. The MOHCC used a combination of vaccination strategies (i.e., fixed and mobile immunization sites, a creche and school-based strategy, and door-to-door activities). Financial costs were estimated at US$ 2.39 per dose, including the vaccine and vaccination supplies (US$ 0.79 operational costs per dose excluding vaccine and vaccination supplies).A mass targeted campaign in densely populated urban areas in Harare, using the recently prequalified typhoid conjugate vaccine, was feasible and achieved a high overall coverage in a short period of time.

Rock mass surface colour is crucial for weathering assessment. CIELAB colour space and Munsell chart are methods to express the surface colour of rock masses. This study analysed the L*a*b* value from both approaches and examined the effectiveness and reliability of rock slope weathering assessment method. The Munsell Rock chart is a conventional method primarily used in practice. However, due to the constraint of individual vision and variation in the optical environment, errors and bias in rock surface colour can easily occur using the conventional method. The colourimeter was used to determine the CIELAB colour values of the samples, while the rock colour chart determined the colour coordinates and Munsell values. The Munsell hue and chroma were assigned using linear interpolation by Munsell conversion software CMC 2.1 to convert Munsell colour systems to L*a*b* value. A total of six granitic rock slopes were investigated. For quantitatively method, the Munsell optical system was less effective in assessing the rock mass surface colour. The positive correlation of a* and b* with R2=0.9407 demonstrated the efficiency of CIELAB system. The a*b* result of the rock slope indicated that most of the slopes were considered medium to strong with a moderately weathered surface. This result is strongly supported by a geomechanical test of Schmidt-UCS and index properties (Id2) with a range of 50-100 MPa and 2-4 MPa respectively. The finding verified mineralogical assessment which showed the correlation of rock mass surface colour to mineral composition. The study recommended any geotechnical and technical purpose in enhancing the method of weathering assessment by using the CIELAB colour space to rapidly and efficiently measure the rock surface colour.

Aim The aim of this study was to compare the efficacy and safety of clindamycin gel + benzoyl peroxide gel and clindamycin gel + adapalene gel in the treatment of mild to moderate acne.

The role of the Al dopant (0.0 to 3.0 wt%) in modifying the structural, microstructural, electrical and optical properties of pulsed laser-deposited ZnO thin films is reported in both as-deposited (AD) and annealed (AN) films. Incorporation of Al3+ ions in the ZnO matrix (AZO) created localized lattice distortions in AD thin films. Breakdown in the local translational symmetry resulted in the observation of otherwise Raman inactive modes in the phonon spectra of the AZO thin films. Furthermore, Al doping enhanced the n-type character of the films, with the charge carrier density exceeding the Mott critical density of ZnO. Charge transport study at low temperatures revealed the metal–semiconductor transition. The increase in charge carrier density with Al doping concentration resulted in a blue shift in the absorption band-edge of these films. These well-characterized thin films were annealed at 800 °C in ambient air for 4 hours. Subsequent characterization revealed drastic modifications in the properties of the AZO thin films. Annealing resulted in reduced lattice distortions, thus improving the crystalline quality of the thin films. This is also supported by the enhanced intensity of E2High phonon mode and the disappearance of Raman inactive modes in the phonon spectra of AN thin films. AN AZO thin films showed reduced charge carrier density and increased resistivity. These radical changes in characteristics suggest that the segregation of Al3+ ions to grain boundaries is a consequence of annealing.

M-type barium hexaferrite (BaFe12O19) is investigated with an aim of using with low temperature co-fired ceramic (LTCC) substrate material. The as-calcined powders from combustion synthesis at neutral and acidic precursor solutions are used, which exhibit excellent properties of low coercive field values (up to 1350 Oe) and high magnetization (up to 60 emu/g). With an appropriate amount of Bi2O3 as sintering aid, high density ferrites have been realized at LTCC processing temperatures. The sintered ferrites possess bulk resistivity in excess of 109 Ω·cm, indicating their suitability for high-frequency applications. Complex magnetic permeability and magnetic loss factors are studied up to 1 GHz frequency. Complex permeability between 1.2 to 2.2 and magnetic loss tangent between 0.05-0.5 have been realized for the sintered ferrites. The influence of Bi2O3 content on resistivity and high-frequency magnetic properties is discussed. It is observed that the sample prepared by employing neutral pH during combustion preparation and calcined at 1200°C for 12 h shows low coercivity of 1350 Oe. After sintering at 900°C with 2 wt% Bi2O3, the sample shows better results with permeability of 1.5-1.7, magnetic loss tangent below 0.3 up to 700 MHz frequency and a high resonance frequency of 140 and 715 MHz in VHF and UHF band, respectively. Since the synthesis conditions provide better control over basic magnetic properties, the use of combustion synthesized BaFe12O19 material augers well for magnetic materials applications in LTCC technology.

The soft chemical route was used in the synthesis of undoped and 5% Mn doped ZnO nanocrystalline powders. XRD, TEM, TGA/DTA, FTIR, and superconducting quantum interference device techniques were used to study the structural, nano/microstructural, thermal decomposition and metastability aspects as a function of calcination temperatures (400–1100 °C) and magnetic properties. The evolution of the major wurtzite phase (ZnO) and minor non-stoichiometric nanocrystalline defect cubic spinel phase (ZnMnO3–δ) at various temperatures is clearly seen. The magnetic hysteresis loop is observed at room temperature in the undoped and doped samples calcined at 400 °C. Interestingly, the hysteresis loop parameters (Ms, Hc) are found to enhance dramatically as soon as the concentration of the minor phase is large enough up to the calcination temperature 700 °C. In contrast, the magnetic hysteresis loop vanishes slowly for the sample calcined at 1000 °C, it disappears completely. The room temperature ferromagnetic behavior at 400 °C is understood in terms of intrinsic cationic/anionic defects, extrinsic defects associated with the various species chemisorbed on the surface of the nanoparticles of undoped and Mn doped ZnO. During thermal annealing a nanocrysatllline seconadary phase of non-stoichiometric defect cubic spinel ZnMnO3–δ is formed, contributing to the enhancement of ferromagnetic behavior. All our experimental results are discussed in terms of model comparing various structural and localized electronic defects formed in the nanocrystalline powder.

Polycrystalline M-type barium hexaferrite (BaFe12O19) samples have been synthesized by solution combustion route at different pH and calcination conditions in order to reduce the coercivity for microwave applications in low-temperature cofired ceramic (LTCC) substrates. Structural, morphological, and magnetic properties of BaFe12O19 were studied by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy, vibrating sample magnetometry (VSM), and Mossbauer spectroscopy. The formation of a single-phase hexagonal structure was confirmed by XRD. The Raman spectra reveal all characteristic peaks of BaFe12O19, illustrating the phase purity and crystal lattice symmetry of the synthesized material. Mossbauer spectra illustrate the existence of Fe3+ cations at all five crystallographic lattice sites. The microstructural features observed by FESEM disclose the growth of nanoregime particles into hexagonal platelet particles after calcination at temperatures from 800°C to 1200°C. The VSM results show a lower coercivity (1350 Oe to 3500 Oe) together with reasonably high saturation magnetization (55 emu/g to 60 emu/g) and a high bulk resistivity (>109 Ω-cm) at room temperature. The dependence of magnetic and electrical properties on the preparation and processing conditions is also discussed.

Undoped and Ga doped ZnO thin films (1% GZO, 3% GZO and 5% GZO) were grown on c -Al 2 O 3 substrates using the 1, 3 and 5 at. wt.% Ga doped ZnO targets by pulsed laser deposition. X-ray diffraction studies revealed that highly c -axis oriented, single phase, undoped and Ga doped ZnO thin films with wurtzite structure were deposited. Micro-Raman scattering analysis showed that Ga doping introduces defects in the host lattice. The E 2 High mode of ZnO in Ga doped ZnO thin film was observed to shift to higher wavenumber indicating the presence of residual compressive stress. Appearance of the normally Raman inactive B 1 modes (B 1 Low , 2B 1 Low and B 1 High ) due to breaking of local translational symmetry, also indicated that defects were introduced into the host lattice due to Ga incorporation. Band gap of the Ga doped ZnO thin films was observed to shift to higher energy with the increase in doping concentration and is explicated by the Burstein-Moss effect. Electrical resistivity measurements of the undoped and GZO thin films in the temperature range 50 to 300 K revealed the metal to semiconductor transition for 3 and 5% GZO thin films.

Pulsed laser deposition was used for growing undoped ZnO and Ga (3 and 5 at. wt.%) doped ZnO thin films on Si (100) substrates with native oxide. X-ray diffraction studies reveal highly c-axis oriented, single phase growth of wurtzite ZnO and Ga doped ZnO thin films. X-ray photoelectron spectroscopy study shows that gallium exists in the Ga3+ oxidation state replacing Zn2+ in the ZnO matrix. It, hence, acts as a donor, increasing the charge carrier density, which was confirmed by Hall measurement. Significant change in the surface morphology of the thin films, such as increased surface roughness, presence of nanostructures, was observed in the Ga doped ZnO thin films. Surface morphology was also influenced by the Ga doping concentration. Higher charge carrier density with the modified surface morphology vindicated its use for field emission studies. Reduction in the threshold field defined for obtaining an emission current density of 0.1 μA/cm2, increased field enhancement factor are features of Ga doped ZnO thin films. The stability of field emission current density of the undoped ZnO and Ga doped ZnO thin films was studied at the preset current density of 2.5 and 2.0 μA/cm2 respectively, for two and half hours.

The changes in the ferroelectric and magnetic properties of the nanostructured Pb(Zr0.52Ti0.48)1-xFexO3 (0 ≤ x ≤ 0.06) due to the doping of different amounts of acceptor ions (Fe3+) have been studied. X-ray diffraction studies show that the system maintains the tetragonal phase up to the doping of 2 mol% of Fe3+ and the formation of secondary phase magnetoplumbite (PbFe12O19) on further doping. Electron paramagnetic resonance studies have revealed the formation of defect centers which in turn arise due to the interaction of Fe3+ ions with oxygen vacancies, which are generated in the lattice. This results in the appearance of room temperature ferromagnetic (RTFM) behavior in the doped samples. The dielectric studies reveal that with the concentration of Fe3+ the peak near the maxima of dielectric constant (e′m) is broadened. Studies of the defect dipoles on the ferroelectric properties have been performed by polarization measurement. The variations of the above properties with the structural and morphological features of the samples have also discussed.

Mn-doped TiO2 nanorods which showed room temperature ferromagnetic (RTFM) behavior have been synthesized by a hydrothermal method. Analysis of X-ray diffraction and Raman spectral data reveal the formation of anatase phase without any impurity phase. From the hysteresis loop measurements, it is possible to estimate the two parameters, magnetization (MS) and coercivity (HC) which are 33 memu/g and 89 Oe respectively, for 5 at% Mn-doped TiO2. The two parameters (MS, HC) are strongly dependent on the Mn doping concentration. The origin of the RTFM is understood in terms of the concentration of oxygen vacancies and/or defects which is created by Mn doping.

The effects of glargine insulin therapy in pregnancies are not well established. We compared maternal and neonatal outcomes of women with pregestational and gestational diabetes treated with glargine or NPH insulin.A prospective cohort study was conducted analyzing outcomes from 56 women with pregestational and 82 with gestational diabetes treated with either insulin regimen.Comparisons were performed among 138 women: 56 with pregestational and 82 with gestational diabetes. In relation to maternal complications, worsening of retinopathy and nephropathy, preeclampsia, micro and macroalbuminuria, and all kinds of hypoglycemia were found higher in women with pregestational diabetes NPH-treated vs. glargine-treated. In women with gestational diabetes NPH-treated, it was observed increased incidence of prepregnancy and new-onset pregnancy hypertension, micro and macroalbuminuria, as well as mild and frequent hypoglycemia, compared to glargine-treated. Among the neonatal outcomes, 1-min Apgar score7, necessity of intensive care unit and fetal death in pregestational, while jaundice and congenital malformations in gestational diabetes, respectively, were more frequently observed in infants born to NPH-treated, compared to glargine-treated.Glargine use during pregnancy from preconception through delivery, showed to be safe since it is associated with decreased maternal and neonatal adverse outcomes compared with NPH insulin-treated patients.

Dye-doped deoxyribonucleic acid-surfactant films have been prepared by an intercalation method and their optical properties have been investigated. Coumarin 1 (C1), known as a neutral laser dye, can be successfully incorporated in deoxyribonucleic acid-surfactant films by immersing them in aqueous dye solution. About 6 wt% C1 can be doped in samples when the immersion time is 86400 s. C1-doped samples show pronounced optical absorption and photoluminescence bands. Not only hydrophobic-hydrophobic interactions but also molecular structures of dyes play prominent roles in the formation of neutral dye-doped deoxyribonucleic acid-surfactant films. It is surmised that C1 stays inside the double helix of deoxyribonucleic acid (DNA) and/or between the alkyl groups of surfactants.

Zinc oxide in the bulk as well as in the nanocrystalline form is thermodynamically stable in the wurtzite structure. However, zinc oxide in the zinc-blende structure is more useful than that in the wurtzite structure due to its superior electronic properties as well as possibility of efficient doping. Therefore, zinc oxide shell is grown epitaxially on zinc sulphide core nanoparticles having zinc-blende structure. It is shown that doping of manganese could be achieved in zinc oxide nanoshell with zinc-blende structure.

Magnetic nanoparticles of iron oxide were synthesized by transferred arc plasma induced gas phase condensation method. Structural, morphological and magnetic studies of the as synthesized powder were carried out using X-ray diffraction, transmission electron microscopy and Mossbauer spectroscopy. These studies have revealed the simultaneous nucleation and condensation of different magnetic phases with a broad size distribution of the nanoparticles which is peaked at 30–50 nm and ranges from 10 nm to 80 nm. 57Fe Mossbauer spectra recorded at various temperatures (5 K–300 K) in presence of external magnetic field (at 5 K) have suggested the presence of different phases of iron oxide with sizable amounts of γ-Fe2O3 and α-Fe2O3 in addition to Fe3O4. The relative concentrations of these phases have been obtained by a self consistent spectral area analysis and were found to be 44:22:34 (%).

Purple acid phosphatase, (PAP), is known to contain dinuclear Fe2 + 2, + 3 site with characteristic Fe + 3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe2 + 2, + 3 (o-NQCH3ox) (o-NSQCH3ox)2 (CAT) H2O]. Fe-2: [Fe + 3(o-NQCH3ox) (p-NQCH3ox)2]2 a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. 57Fe Mossbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. 57Fe Mossbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe + 3]A and [Fe + 2]B sites. The hyperfine interaction parameters are δ A = 0.152, (ΔE Q)A = 0.598 mm/s with overlapping doublet at δ B = 0.410 and (ΔE Q)B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe + 3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQCH3ox ligand surrounding Fe + 3(h.s.) state generates small field gradient indicated by quadrupole split ΔE Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe2 + 2, + 3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g 1 = 4.17 and g 2 = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe + 3(h.s.) configuration. SQUID data of \(\chi _m^{{\rm corr}} \mbox{.T}\) were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = −13.5 cm − 1 with an agreement factor of R = 1.89 × 10 − 5). The lower J value of antiferromagnetic exchange leads to Fe+3μ-(OH) Fe + 2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe + 3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = −12.4 cm − 1, g = 2.3 with R = 3.58 × 10 − 5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.

Microwave-hydrothermal (MH) route was employed to synthesize various iron oxide phases in ultra-fine crystalline powders by using ferrous sulphate and sodium hydroxide as starting chemicals. All chemical reactions were carried out under identical MH conditions, namely, at 190°C, 154 psi, 30 min, by varying the molar ratio (MR) of FeSO4/NaOH in the aqueous solutions. The variation of MR has a dramatic effect on the crystallization behavior of various phases of iron oxides under MH processing conditions. For example, spherical agglomerates of Fe3O4 powder were obtained if MR equal to 0.133 (pH>10 sample A). On the other hand non-stoichiometric Fe3O4 powders (Sample B) were obtained for all higher MR of FeSO4/NaOH between 0.133 and 4.00 (6.6

The modifications in electrical and magnetic properties of polycrystalline bulk La 0.7 Ca 0.3 Mn 1− x T x O 3 (T=Fe, Ga) samples at relatively higher doping concentration ( x =0.08–0.12) are investigated. All the synthesized, single phase samples were subjected to resistivity measurements in the temperature range 50–300 K. No insulator–metal transition ( T P ) was observed for Fe doped samples with x =0.12. For all the other samples the transition temperature decreased with increase in doping concentration. The small polaron hoping energy was found to increase, rather slowly, with increase in doping concentration. The effect on magnetic properties is also prominently observed with respect to doping element and doping concentration. Interestingly, with the increase in doping concentration, the Curie temperature ( T C ) and T P separate out significantly indicating decoupling of electric and magnetic properties. Changes in these properties have been analyzed on the basis of magnetic disorder introduced in the system due to the magnetic and nonmagnetic nature of these ions rather than strong lattice effects which is insignificant due to similar ionic radii of Fe +3 and Ga +3 when compared to that of Mn +3 .

Magnetic multilayers have attracted much attention due to their potential applications in spintronic devices because of their ability to inject spin-polarized current. The bilayer of ferrimagnetic Fe3O4 and manganites La0.7Ca0.3MnO3 (LCMO) is an interesting system due to the (i) fascinating electrical and magnetic properties of the spinel and perovskite material and (ii) high-spin polarization character of Fe3O4. In this work, we report our results on pulsed laser deposited thin films of Fe3O4/LCMO bilayer on LaAlO3 (LAO) substrate. For comparison, LCMO and Fe3O4 films were also grown on LAO substrate separately. The films were characterized by techniques such as X-ray diffraction, four-probe electrical resistivity with and without magnetic field. It is shown that oriented Fe3O4/LCMO bilayer can be grown successfully on the c-axis oriented LAO substrate. The electrical transport properties suggest that at low temperature the junction shows considerable magnetoresistance.

Films of nanocrystalline γ-Fe2O3 were deposited on silicon substrates by using the technique of electrophoretic deposition. The precursor powder was nanocrystalline γ-Fe2O3, which was synthesized, using DC arc plasma in the oxygen ambient by vapour–vapour interaction in gas phase condensation; at a stabilized arc current of 40 A. This powder was characterized by X-ray diffraction, Transmission Electron Microscopy, Vibrating Sample Magnetometer and Mossbauer Spectroscopy. An increase in directional coercivity was observed in case of films deposited on silicon substrates, which is dramatically significant. Preferred orientation of almost similar sized nanocrystalline magnetic domains in deposited films is evident from the results of X-ray diffraction and Transmission Electron Microscopy results. The preferred alignment of the nanocrystallites seems to be responsible for the significant changes observed in magnetic properties of films.

Polycrystalline bulk samples of La1–XBaXMnO3 (x = 0.5 – 0.65) were synthesized by solid state reaction route. Low temperature four probe resistivity measurements and a.c. susceptibility measurements were carried out on these samples after the analysis of powder XRD data with Rietveld fitting method. All the studied compounds showed paramagnetic to ferromagnetic transition at TC ∼ 330 K and also showed insulator-metal transition (at temperature TP) with no indication of charge-ordering. In La1−xBaxMnO3 case the insulator-metal transition is well below the magnetic transition. At x = 0.55, the difference in TP and TC is ∼ 90 K and also XRD pattern starts showing the existence of BaMnO3 phase which grows with x. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Polycrystalline Ni-Zn ferrite, with a well-defined composition, $Ni_{0.8}Zn_{0.2}Fe_{2}O_4$, synthesized by a low temperature method showed the formation of a cubic ferrite phase with a crystallite size of 15 nm and saturation magnetization of Ms ≈ 44 emu/g at room temperature. When calcined at higher temperatures (up to 1200 oC) the magnetization increased continuously to Ms ≈ 67 emu/g. To understand the magnetic nature of the cubic ferrite phase formed at a temperature as low as 80 oC, 57 Fe Mossbauer spectra were recorded for samples annealed at three different temperatures, without any external magnetic field, and with an external field of $H_ext$ = 5 T, at 4.2 K. The spectral parameters at room temperature, namely, isomer shift, quadrupole splitting and hyperfine field, confirmed the presence of ultrafine superparamagnetic crystallites of Ni-Zn ferrite. The Mossbauer spectra at 4.2 K revealed spin relaxation effects resulting in very broad sextets, characteristic of ultrafine crystallites. The Mossbauer spectra recorded at 4.2 K and $H_ext$ = 5 T showed well resolved two sextet pattern with characteristic hyperfine interaction parameters of the cubic ferrite phase.

Metastable ferromagnetic phases, for different compositions in La2MnCo1−xNixO6, are obtained for samples synthesized by a low-temperature method and annealed in air at different temperatures in the range 200–1350 °C. The Tcs of the ferromagnetic phases vary linearly between those of the phases of the end members. Tcs of the different phases of La2MnCo1−xNixO6 can be predicted based on the Tcs and spin states of Mn, Co and Ni in the different phases of the end members, La2MnCoO6 and La2MnNiO6.

The concentration on Cu 2 O (Cu 2 O=1, 2, 3 and 4 wt.%) powder-dependent gas-sensing performance of δ-Al 2 O 3 /Cu 2 O material screen-printed on α-Al 2 O 3 substrates and heated at 750 °C/1 h is evaluated systematically. For this purpose, nanocrystalline δ-Al 2 O 3 (15–20 nm) powder prepared by DC IS plasma technique was used as a functional material. Resultant δ-Al 2 O 3 /Cu 2 O samples were characterized by XRD, scanning electron photomicrograph (SEM) and Half bridge method. The characterization studies revealed that the sensitivity factor (SF) decreases with increase in additive weight percentage of Cu 2 O for all the three gases of CO, H 2 and LPG. It shows maximum SF of 165, 296 and 78 for CO, H 2 and LPG gases (1000 ppm each), respectively, at an optimum operating temperature ( T opt. ) of 450 °C for 1 wt.% of Cu 2 O. All the gases show flat response for all concentration values of Cu 2 O at the above 2 wt.%. Thus, the present material (δ-Al 2 O 3 /Cu 2 O, Cu 2 O=1 wt.%) shows more selectivity for H 2 gas over LPG compared to CO ( S H 2 / S CO =1.8 and S H 2 / S LPG =4.3). The particle size of δ-Al 2 O 3 /Cu 2 O samples was found to be in the range of 0.05–0.5 μm.

Synthesis of La 0.5 Ba 0.5 MnO 3 powder by microwave-hydrothermal (MH) accelerated solid state reaction (SSR) route is reported. In this method, SSR is accelerated by use of MH route. MH route decreases the formation temperature to 900 °C and reaction time to 8 h when compared to 1400 °C and 48 h, respectively, for conventional solid state reaction method. The materials are characterized by powder XRD, SEM, TEM, temperature dependence of AC susceptibility and four-probe magnetoresistance technique in a magnetic field of 1 T. XRD data show the formation of the desired phase without any secondary phases. SEM studies reveal agglomeration nature of primary particles with agglomerate size ∼1 μm and the TEM picture supports SEM analysis. AC susceptibility, resistivity in the absence of magnetic field ( ρ 0 ) and in the presence of the field ( ρ H ) and magnetoresistance: MR=[( ρ 0 − ρ H )/ ρ 0 ] all show a peak or a small structure at ∼200 K indicative of a magnetic phase transition at this temperature.

The effect of variation of sintering temperature (600–800 °C/4 h) on the gas sensing characteristics of a SnO 2 :Cu (Cu=9 wt.%) system (a high-performance temperature-selective composition) in the form of pellets is investigated systematically for the CO, H 2 and LPG gases at a concentration level of 1000 ppm. The XRD, SEM and half-bridge techniques were employed to establish the structural, morphological and gas sensing characteristics of the materials, respectively. A very high value of sensitivity factor (SF) equal to 1400 is obtained for CO gas at an optimal operating temperature of 160 °C for the pellets sintered at 750 °C. The selectivity values of CO gas against H 2 and LPG ( S CO / S H 2 ∼14 and S CO / S LPG ∼280) at an optimum temperature of 160 °C are also improved considerably. This material (SnO 2 :Cu, Cu=9 wt.% sintered at 750 °C with an optimal temperature of 160 °C) may prove to have tremendous potential for CO gas sensing applications.

The role of the trivalent rare-earth ion on the paramagnetic to ferromagnetic transition temperature (Tc) of the substituted perovskite-type rare-earth (R) manganese oxides, RMn0.5Co0.5O3 and RMn0.5Ni0.5O3 (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er and Yb), is compared. For a particular R3+ with larger ionic size, the Tc of RMn0.5Ni0.5O3 is larger than that of RMn0.5Co0.5O3 and vice versa for smaller ionic size, though the ionic sizes of trivalent low-spin Co and Ni ions are comparable. Tc values of both Co and Ni containing compositions decrease with the decrease in the ionic size of R3+, showing a faster decrease for heavier rare-earth ions beyond Gd3+. Though the decreasing size of the rare-earth ion is responsible for the decrease in the magnetic transition temperature, due to structural distortions, an anomalous change in the rate of decrease of Tc beyond Gd3+ is due to contributions from the single-ion anisotropy of the heavier rare-earth ions.

The effect of substitution of Fe for Co in the high- T c phase of ferromagnetic LaMn 0.5 Co 0.5 O 3 , containing Mn 3+ and low-spin Co 3+ ions, is studied to understand why ferromagnetism is not observed in the related compound LaMn 0.5 Fe 0.5 O 3 . The ferromagnetic transition of LaMn 0.5 Co 0.5 O 3 is found to be broadened, with a decrease in the magnetization, as Fe is gradually substituted for Co in LaMn 0.5 Co 0.5− x Fe x O 3 . The unit cell lattice parameters vary linearly for x >0, following Vegard's law, indicating the possibility of a random distribution of the B-site ions in the perovskite lattice on Fe substitution. The observed magnetic behavior of LaMn 0.5 Co 0.5− x Fe x O 3 (0 x ⩽0.5) can be best described in terms of random site percolation.

Systematic evaluation of gas-sensing characteristics of Cu-modified SnO 2 pellets for CO, H 2 and CH 4 gases from ppm to percentage level is reported. The concentration level of Cu additive was varied systematically from 1 to 11 wt %. The highest values of sensitivity factor (SF) of 240 and 590 corresponding to CO and H 2 gases were obtained at considerably lower temperatures of 160 and 230 °C, respectively, for 9 wt.% of Cu. The selectivity values are found to be maximum at 7 and 9 wt.% of Cu for H 2 (≈78) and CO (≈1.9) gasses, respectively. For CH 4 gas, on the contrary, the sensor showed quite inferior response. The sensitivity curve for our material follows the usual trend of three-region behaviour of standard Windischmann and Mark's curve. The sensor tends to saturate at 1.5% and 3.6% for CO and H 2 , respectively. XRD and scanning electron micrograph (SEM) characterisation techniques are used to pinpoint the possible reasons for high performance of the sensor at 9 wt.% Cu. Our sensor material showed promising properties for gas-sensing (CO and H 2 ) applications.

Barium–strontium titanyl oxalate (BSTO) [Ba 1− x Sr x TiO(C 2 O 4 ) 2 ·4H 2 O with x =0.25 precursor powders] were prepared successfully by using the simple chemical exchange reaction between oxalotitanic acid (HTO) [H 2 TiO(C 2 O 4 ) 2 ·2H 2 O], barium hydroxide and strontium nitrate at room temperature. Initially, oxalotitanic acid was prepared by using the reaction between 0.1 M titanium tetrabutoxide and 0.2 M oxalic acid in isopropanol (IPA). Barium hydroxide and strontium nitrate were added directly to this solution in stoichiometric amounts. The required solubility achieved only after addition of distilled water dropwise leads to the controlled precipitation of BSTO molecular precursor. To maintain the equilibrium (pH conditions), more and more Ba(OH) 2 and Sr(NO 3 ) 2 solids get dissolved and reaction continues. The kinetics of exchange reaction is governed by the rate of addition of water. The pyrolysis of BSTO at 750 °C/4 h in air produced the Ba 1− x Sr x TiO 3 (BST) powders. The characterization studies were carried on the as-dried and calcined powders by various physicochemical techniques viz. microanalysis, chemical analysis, DTA/TGA, XRD, IR, scanning electron microscopy (SEM), etc. It revealed that the BST powders are cubic, stoichiometric, highly pure with yield>99% and agglomerated nature (size: 0.5–2 μm).

The perovskite-type oxide La2MnCo0.5Ni0.5O6 has been found to form in three different ferromagnetic phases with different transition temperatures, when a low-temperature synthesized sample is annealed at different temperatures. The interesting magnetic behaviour of the compound is due to the combination of different spin states of Mn, Co and Ni in the different phases of the compound. The magnetic transition temperatures of the three phases of the compound can be predicted from the Tc s of La2MnCoO6 and La2MnNiO6.

The GNP route has been successfully employed to generate nanosized, porous, stoichiometric, homogeneous Ce0.75Zr0.25O2 powders. In this route, a precursor solution is prepared by mixing glycine with an aqueous solution of mixed (Ce–Zr) metal–nitrates in their stoichiometric ratios. Initially, the glycine mixed precursor solution was heated in a petri dish to evaporate the excess water to form a viscous semitransparent material. Then the petri dish was kept in a 5-l capacity beaker covered with a metallic mesh and then the temperature was increased slowly to 190–200 °C to autoignite the material. The combustion was self-sustaining and very rapid, producing yellowish coloured powders. The as-prepared powders were nanosized (20–35 nm), having a spherical shape, and were crystallized in cubic fluorite structure with lattice parameter a0=5.38 A. The powders showed a very wide pore size distribution in the range of 20–2500 A as is shown by mercury porosimetry measurements with surface area ≈40.0 m2/g. No change in crystalline phase was observed even after giving heat treatments to as-prepared powders up to 1000 °C for 4 h in air .The SEM/TEM studies on these powders confirmed their nanosized nature with porous structure.

Submicron-sized (0.15–0.2 μm) spherical agglomerates of magnetite (Fe3O4) powders have been prepared successfully by microwave hydrothermal (MH) reaction of ferrous sulphate and sodium hydroxide in the temperature range of 90–200 °C. X-ray powder diffraction patterns of all these powders indicated that the product is single-phase magnetite with cubic spinel structure having lattice parameter, a0=8.392 A. The Mossbauer spectra of these powders indicated that stoichiometric Fe3O4 particles are obtained only when molar ratio of Fe/NaOH≥0.133 is maintained in the solution. It is observed that Fe/NaOH ratio is an important parameter for the controlled oxidation of ferrous salts in alkaline media under MH condition to produce stoichiometric Fe3O4. Further, the kinetics of MH synthesis is one order faster than the reported conventional hydrothermal (CH) synthesis. The value of saturation magnetization M=70 emu/g is obtained in case of stoichiometric Fe3O4. However, when ferric salt is treated in alkaline medium single-phase α-Fe2O3 is obtained under the MH conditions of 200 °C (194 psi).

A chemical co-precipitation route is developed to precipitate mixed oxalates (PbC 2 O 4 +TiOC 2 O 4 .2H 2 O) at room temperature. In this synthesis route, an anionic TiO(C 2 O 4 ) 2 −2 species obtained by dissolving potassium titanyl oxalate (KTO) (0.01 M) stable over narrow pH range are destabilized with the addition of 0.01 M solution of lead chloride (PbCl 2 ) to produce insoluble TiOC 2 O 4 .2H 2 O and oxalic acid. The in situ generated oxalic acid during destabilization process reacts with Pb 2+ ions to precipitate lead oxalate (PbC 2 O 4 ). The mixed oxalates on pyrolysis in air at 750 °C/4 h produced submicron sized (0.13–0.15 μm) stoichiometric PbTiO 3 (PT) powders having tetragonal symmetry (with c / a ratio ∼1.063) which form agglomerates of size 0.5–5 μm. Various physico-chemical techniques were used to characterize the as-dried mixed oxalates precursor and PbTiO 3 powders . All these experimental results related to synthesis and characterization of these powders are presented in this paper.

Studies on a large number of compositions among the ferromagnetic self-doped manganites, La1−xMnO3, show that the ferromagnetic Curie temperature increases with x and reaches a maximum value for x = 1/7. Tc remains independent of x for x ≥ 1/7 and the maximum value of the magnetization is obtained for x = 1/8. The presence of a second phase, due to Mn3O4, whose contribution increases with x, is observed in the powder x-ray diffraction patterns for x > 1/8 and the lattice parameters remain independent of x for x > 1/8. The results indicate that the limiting value of x or the extent of self-doping possible in La1−xMnO3 is x = 1/8.

A self-sustaining controlled acid–base reaction between oxalotitanic acid [H2TiO(C2O4)2] (HTO) and barium hydroxide [Ba(OH)2� 8H2O] at room temperature is utilized for the quantitative precipitation of barium titanyl oxalate (BTO). For this purpose, an intermediate soluble oxalotitanic acid precursor is generated by reacting 0.1 M solution of titanium tetrabutoxide in isopropanol (IPA) with 0.2 M solution of oxalic acid in IPA. Equimolar suspended Ba(OH)2 particles in IPAwere mixed with the above-mentioned oxalotitanic acid solution. The self-sustaining acid–base reaction between Ba(OH)2 and H2TiO(C2O4)2 was initiated only when necessary amount of water was added. This shift from non-aqueous to semi-aqueous condition allows a required solubility of Ba(OH)2, which makes Ba 2+ ions available for the exchange reaction. The solubility of Ba(OH)2 and its dissociation governs the kinetics of the reaction leading to the precipitation of BTO with yield z99%. The controlled pyrolysis of BTO at 750 jC/4 h in air-produced agglomerated cubic BaTiO3 powders having spherical particles with size c100 nm. These powders are sintered in the form of pellets at 1300 jC/4 h to obtain compacts with density c95%. These compacts showed dielectric constant eRT=1680 (tandV2%), emaxc7780 at TC=121 jC. D 2002 Elsevier Science B.V. All rights reserved.

We have investigated whether size of the doped ions is the crucial factor controlling the formation and stability of single phase compounds with tetravalent ions substituted in the A-site of the rare earth perovskite manganite, LaMnO 3 . These studies are carried out based on the recent controversial reports in the literature on the substitution of smaller tetravalent ions Ce 4+ and Sn 4+ for the trivalent ion La 3+ . The tetravalent ion, Th 4+ , is selected for the studies because of its larger ionic size (1.05 A) when compared to that of Ce 4+ (0.97 A) and Sn 4+ (0.81 A). Moreover, the ionic size of Th 4+ is comparable to that of Gd 3+ (1.053 A) which is a typical A-site cation in the perovskite manganite and can also be substituted for La 3+ (1.16 A). It has been observed that a nominal composition, La 0.7 Th 0.3 MnO 3 , synthesized by the usual procedure, contains different phases as La 0.7 MnO 3 , ThO 2 and Mn 3 O 4 . From powder X-ray diffraction and magnetic measurements, and by comparing with the results on Ce 4+ and Sn 4+ substituted compositions in different reports, it is concluded that generally it is not possible to substitute the trivalent La 3+ ion by a tetravalent ion, due to the ionic size constraints, valency of Mn and site preferences of different ions.

Studies on different LaMnO3+δ samples have revealed that there is no correlation between the magnetic properties and large values of δ (Mn4+ content) or the rhombohedral structure of the material. From powder x-ray diffraction studies, it was found that those LaMnO3+δ samples showing well defined ferromagnetic transitions are of mixed-phase character: an La1-xMnO3+δ phase and minor amounts of an La-rich phase. The results give sufficient evidence to conclude that the self-doped, La-deficient, phases formed are responsible for ferromagnetism in LaMnO3+δ.

Binary mixed metal oxides, having composition Ce0.75Zr0.25O2 were prepared by microwave–hydrothermal (MH) reaction (200 °C, 200 psi, 30 min) using ZrO(NO3)2·xH2O, Ce(NO3)3·6H2O as starting precursors and KOH as mineralizer. 0.025, 0.075 and 1.2 M solutions of ZrO(NO3)2·xH2O, Ce(NO3)3·6H2O and KOH, respectively, are used for MH synthesis. Solution (7.5 ml) of each of ZrO(NO3)2·xH2O (0.025 M) and Ce(NO3)3·6H2O (0.075 M) are mixed with 25 ml of KOH and treated in specially designed vessels using microwave accelerated reaction system to obtain ceria–zirconia solid solution. Various physico-chemical techniques such as XRD, Raman, SEM, EDAX, TEM, BET, etc. are used to characterize the resultant powders. The results showed that the as-prepared powder particles consisted of solid solution of ceria–zirconia having cubic fluorite structure with surface area equal to 125 m2 g−1. SEM/TEM photographs for the same showed varied distribution of agglomerates with primary particle size≅7 nm. The cubic phase is obtained at a temperature (pressure) and time as low as 180 °C (127 psi) and 5 min.

Rubber ferrite composites have the unique advantage of mouldability, which is not easily obtainable using ceramic magnetic materials. The incorporation of mixed ferrites in appropriate weight ratios into the rubber matrix not only modifies the dielectric properties of the composite but also imparts magnetic properties to it. Mixed ferrites belonging to the series of Mn(1 -x)Znx Fe2 O4 have been synthesised with different values of x in steps of 0·2, using conventional ceramic processing techniques. Rubber ferrite composites were prepared by the incorporation of these pre-characterised polycrystalline Mn(1 -x)ZnxFe2 O4 ceramics into a natural rubber matrix at different loadings according to a specific recipe. The processability of these elastomers was determined by investigating their cure characteristics. The magnetic properties of the ceramic fillers as well as of the rubber ferrite composites were evaluated and the results were correlated. Studies of the magnetic properties of these rubber ferri...

In Mn1−xZnxFe2O4 (x=0 to 1) nanosize particles prepared through hydrothermal precipitation we observe a decrease in particle size from 13 to 4 nm with increasing Zn concentration from 0 to 1. The lattice constant, a, for all Mn/Zn concentrations is found to be less than that for the corresponding bulk values. At specific compositions within x=0.35 and 0.5, the temperature dependence of the magnetization exhibits a cusp-like behavior below the temperature at which the nanoparticles undergo a ferri- to para-magnetic transition (Tc). The Curie temperatures, Tc, of the nanoparticles are in the range of 175–500 °C, which are much higher than their corresponding bulk values. To explain these unusual features, the strong preferential occupancy of cations in chemically inequivalent A and B sites and the metastable cation distribution in nanoparticles are invoked.

The endocrine-disrupting effects of styrene dimers (SD: NSD-01, -08 and -09) and styrene trimers (ST: NST -01, -03 and -12), which migrated from polystyrene (PS) containers into instant food, were investigated together with styrene monomer (SM) using in vitro and in vivo assays. In the estrogen (ER) and androgen receptor (AR) binding assay, SM, SD and ST showed no binding activity at concentration of 10(-10)-10(-5) mol/l. In order to evaluate the estrogenic activity in vivo, the uterotrophic assay was conducted. When prepubertal and ovariectomized adult rats were dosed with SM, SD and ST for 3 days by subcutaneous injection, these compounds did not induce significant increase in uterine weight. Additionally, to evaluate anti-androgen activity in vivo, the Hershberger assay for anti-androgenic activity in the presence of testosterone treatment was conducted. When castrated, testosterone-treated immature male rats were dosed SM, SD and ST for 7 days by oral gavage, these compounds did not induce a decrease in the seminal vesicle, ventral prostate and levator ani plus bulbocavernosus muscle weights. To evaluate the effects on hormones other than sex hormones, the thyroid hormone receptor (TR) binding assay and rat serum prolactin (PRL) was conducted. In the TR binding assay, SM, SD and ST showed no binding activity at a concentration of 10(-5) mol/l. When ovariectomized rats were dosed with SM, SD and ST for 3 days by sc injection, the results showed there was no change in rat serum PRL. From the above these results, we concluded that SM, SD and ST exhibit no apparent estrogenic, androgenic, anti-androgenic and thyroid activity.

The effect of R on the ferromagnetic Curie temperatures of two different phases of RMn 0.5 Co 0.5 O 3 (R=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) has been studied. For both high- T c and low- T c phases of RMn 0.5 Co 0.5 O 3 , T c decreases with decreasing ionic radius of R 3+ and the tolerance factor. The rate of decrease of T c is larger for the high- T c phases containing Mn 3+ and low-spin Co 3+ when compared to the low- T c phases containing Mn 4+ and Co 2+ , indicating that the Mn 3+ –O–Mn 3+ superexchange interactions are more susceptible to internal pressure effect of R 3+ when compared to the effect on the Mn 4+ –O–Co 2+ superexchange interactions.

Evidence for an unusual double charge disproportionation, Mn4+ + Co2+ → Mn3+ + Co3+ → Mn4+ + Co2+, is observed in nanocrystalline LaMn0.5Co0.5O3 synthesized by a low-temperature method and annealed in the temperature range 200–1300 °C. The Curie temperature of nanocrystalline LaMn0.5Co0.5O3 is increased from 150 to 230 K when annealed in the temperature range 200–700 °C and is further decreased back to 150 K when annealed in the temperature range 700–1300 °C. This increase and decrease in Tc is found to be associated with the conversion of the spin states of Mn and Co from Mn4+ and Co2+ to Mn3+ and low-spin Co3+, and again back to Mn4+ and Co2+ as evidenced from x-ray photoelectron spectroscopic studies.

A simple chemical route is developed to obtain an important molecular precursor (leading to barium titanate powders), namely barium titanyl oxalate (BTO) with nearly theoretical yield. In this route, 0.1 M alcoholic solution of titanium tetrabutoxide is reacted with 0.1 M alcoholic solution of oxalic acid to form titanyl oxalate (TiOC2O4). This was further converted to soluble ammonium titanyl oxalate (ATO); (NH4)2TiO(C2O4)2.H2O by reacting with an equimolar aqueous solution of ammonium oxalate (pH 4.25). Instead of using available barium salts (halide/nitrate/acetate) solution, a modified barium precursor solution with controlled pH (=4.2) is prepared for carrying out cation-exchange reaction with ATO. For this purpose the modified Ba-precursor solution is freshly prepared by partial neutralization of a 0.1 M aqueous solution of barium hydroxide with controlled addition of dilute HNO3 (1.1 M) solution. The pH of this solution is the same as that of the ATO solution. The exchange reaction between equimolar ATO and modified Ba-precursor solution precipitated barium titanyl oxalate (BTO) with a quantitative yield at room temperature. Submicron-sized, stoichiometric, pure BaTiO3 powders were obtained by the controlled pyrolysis of BTO in air. The present communication deals with the detailed analysis of this simplified method in producing BTO/BT powders and their characterization employing various physicochemical techniques.

An improved chemical route is described to precipitate quantitatively a molecular precursor lead zirconyl oxalate tetrahydrate, PbZrO(C 2 O 4 ) 2 ·4H 2 O (PZO) at room temperature. In this route, soluble ammonium zirconyl oxalate, (NH 4 ) 2 ZrO(C 2 O 4 ) 2 (AZO), is initially prepared by chemical reaction of 0.1-M solution of zirconyl nitrate with 0.2-M solution of ammonium oxalate. The anionic species ZrO(C 2 O 4 ) 2 −2 thus obtained is exchanged by adding equimolar solution of lead acetate to precipitate single-phase PZO with higher yield. The improvement in the presently described route is to drive exchange reaction to its completion by suitably manoeuvring the choice of precursor, pH and reaction conditions, in such a way that single-phase PZO is precipitated without any destabilization of anionic species ZrO(C 2 O 4 ) 2 −2 . The pyrolysis of PZO produced stoichiometric, monophasic, orthorhombic PbZrO 3 (PZ) powders at temperature T =700°C. Various physico-chemical techniques were used to characterize both molecular precursor PZO as well as PZ powders obtained by its pyrolysis. All our experimental results related to the synthesis and characterization of these powders are presented in this paper.