Search

This work reports magnetic field direction dependent second magnetisation peak (SMP) anomaly in single crystals of oxygenated for ab. Detailed investigations on crystal A revealed the direction dependence of SMP anomaly at temperatures below 25 K, above which the direction dependence vanishes. The state of spatial order of the vortex lattice was found to be correlated to the vortex lattice symmetry that underwent a change at certain fields and was captured via single flux jumps observed in the third and fifth quadrant of magnetisation hysteresis loops. Bean's critical state profiles drawn to explain the flux jumps required the presence of clusters of in the basal plane of with closely lying binding energies. Large full width at half maximum observed in Cu, O, Y and Ba photoelectron spectra confirmed the validity of the proposed cluster model. A vortex phase diagram incorporating all features in the magnetisation hysteresis loops has been made for oxygenated for || ab depicting various phases. [ABSTRACT FROM AUTHOR]

Sensing and quantification of gas at low concentrations is of paramount importance, especially with highly flammable and explosive gases such as hydrogen. Standard gas sensing setups have a limit of measuring ultra-low concentrations of few parts per billion unless the external gas cylinders are changed to ones with low concentrations. In this work, we describe a home-built resistance based gas sensing setup that can sense across a wide concentration range, from parts per billion to parts per million, accurately. This was achieved using two dilution chambers: a process chamber and a feedback assembly where a part of the output gas from the dilution chamber is fed back to the inlet mass flow controller, enabling enhanced dilutions without increasing the number of mass flow controllers. In addition, the gas-sensing setup can measure across a large temperature range of 77–900 K. The developed setup was then calibrated using palladium thin films and ZnO nanoparticle thin films. The setup was tested for reproducibility, concentration response, temperature response, etc. Corresponding sensitivity values were calculated and found to be in good agreement with published values, validating our setup design. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate how the metal–citrate complex structure formed in the gel reflects the true stoichiometry of the redox mixtures to yield a highly dense BaZrO3 ceramic obtained as a combustion product in the sol‐gel autocombustion technique. By systematically varying the citric acid to metal cation ratio (C/M) between 0.56, 1.0, 1.5, and 2, we show that the optimal synthesis parameters correspond to C/M ratio of 1.5, at which ratio complete chelation of citrates happen with nitrates. This was confirmed using TGA, which showed a single‐step weight loss peak corresponding to C/M =1.5 but multiple peaks in C/M ratios of 0.56 and 1. PXRD and FTIR measurements on all the burnt powders showed multiphase peaks for the C/M ratios 0.56 and 1 but only peaks corresponding to BaZrO3 for C/M = 1.5, apart from a very tiny BaCO3$_3$ peak. Combustion behavior of each sol‐gel corresponding to C/M ratios 0.56, 1.0, 1.5, and 2.0 is described in detail, wherein 0.56 and 1.0 sol‐gels were found to belong to the smouldering/less intense flame‐type combustion, while 1.5 and 2 belonged to the intense flame combustion, contradicting oxidant to reductant ratio (O/R) calculations that require a stoichiometric combustion for C/M ratio of 0.56 to result in an intense flame combustion. This discrepancy was explained by the optimal usage of NO3−$_3^-$ ions in the gel structure corresponding to C/M ratio of 1.5 since a complete chelation of citrates to nitrates ions happen for C/M = 1.5. The observed combustion behavior, phase purity, and other characteristics of stoichiometric/ nonstoichiometric combustion products are illustrated by means of the extent of the 3D metal–citrate complex network formed as a function of C/M. The density of the sintered pellets that were sintered at a temperature of 1650∘$^\circ$C was found to be the best at 99.6%$\%$ for the C/M ratio 1.5. This is the highest ever reported density for BaZrO3 ceramic demonstrating that C/M ratio of 1.5 represents that metal to cation ratio for which best chelation of citrates happen with nitrates resulting in the formation of dense BaZrO3 ceramics. A comparison of BaZrO3$_3$ pellet made by solid‐state synthesis technique yielded a low value of density of 97.5%$\%$. Impedance spectroscopy measurements done on all BaZrO3$_3$ pellets yielded the lowest grain‐boundary resistance for the pellet made by the sol‐gel technique with C/M ratio of 1.5. [ABSTRACT FROM AUTHOR]

This work reports the synthesis, structure and magnetic properties of a facile spin 1/2 one dimensional Heisenberg antiferromagnet bis(4-aminopyridinium) bis(oxalato)cuprate(II) dihydrate, (C5H7N2)2[Cu(C2O4)2]·2H2O. Single crystals of large sizes of the title compound were obtained using the technique liquid–liquid diffusion or layer diffusion with 100% yield. Single crystal X-ray diffraction measurements revealed the very good quality of the grown single crystals with a small value of goodness of fit R obtained (1.058). Powder X-ray diffraction showed the presence of peaks of the main phase with no impurity peaks, confirming the good quality of the crystals. The structure comprises corner sharing CuO6 octahedra resulting in Cu–Cu chains in the a-direction that are very well isolated in the b and c directions. Density functional theory (DFT) calculations with three different basis sets (B3LYP/6-311++G(d,p); B3LYP/LanL2DZ and B3LYP/6-311++G(d,p), B3LYP/LanL2DZ) generated the optimized geometry of a monomeric unit as well as its vibrational spectra. A vibrational frequency corresponding to the CuO6 octahedron was found in the experimentally obtained FTIR spectrum that matched very well with the theoretically obtained IR spectra incorporating the mixed basis. Temperature dependent dc magnetic susceptibility measurements revealed a low temperature peak, suggesting the presence of low dimensional magnetism in the system. Bonner–Fisher fit confirmed the one dimensional nature of the magnetic interaction with an exchange coupling constant of 1.23 K. Magnetisation measurements along with quantum Monte Carlo simulations confirm this metal–organic crystal to be a very good spin-1/2 Heisenberg antiferromagnet with a low saturation field Hs of 1.75 T. [ABSTRACT FROM AUTHOR]

The redox reaction of oxygen (OER & ORR) forms the rate determining step of important processes like cellular respiration and water splitting. Being a spin relaxed process governed by quantum spin exchange interaction, QSEI (the ground triplet state in O 2 is associated with singlet oxygen in H 2 O/OH - ), its kinetics is sluggish and requires inclusion of selective catalyst. Functionality and sustainability of solid oxide cell involving fuel cell (FC) and electrolyzer cell (EC) are also controlled by ORR (oxygen redox reaction) and OER (oxygen evolution reaction). We suggest that, presence of inherent spin polarization within La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3- δ (LSCF6482) (15.86 emu g -1 ) and Ba 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3- δ (BSCF6482) (3.64 emu g -1 ) accounts for the excellent selective electrocatalysis towards ORR and OER. QSEI forms the atomic level basis for OER/ORR which is directly proportional to spin ordering (non-zero magnetization) of the active electrocatalyst. LSCF6482 exhibits (21.5 kJ mol -1 @0.8 V for ORR compared to 61 kJ mol -1 @0.8 V for OER) improved ORR kinetics whereas BSCF6482 (18.79 kJ mol -1 @0.8 V for OER compared to 32.19 kJ mol -1 for ORR@-0.8 V) is best suited for OER under the present stoichiometry. The findings establish the presence of inherent spin polarization of catalyst to be an effective descriptor for OER and ORR kinetics in solid oxide cell (SOC)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

ZnO is a widely studied gas sensor material and is used in many commercial sensor devices. However, selectivity towards any particular gas remains an issue due to lack of complete knowledge of the gas sensing mechanism of oxide surfaces. In this paper, we have studied the frequency dependent gas sensor response of ZnO nanoparticles of a diameter of nearly 30 nm. A small rise of synthesis temperature from 85 °C to 95 °C in the solvothermal process, shows coarsening by joining and thereby distinct loss of grain boundaries as seen from transmission electron micrographs. This leads to a substantial reduction in impedance, Z (GΩ to MΩ), and rises in resonance frequency f res (from 1 to 10 Hz) at room temperature. From temperature dependent studies it is observed that the grain boundaries show a Correlated Barrier Hopping mechanism of transport and the hopping range in the grain boundary region is typically 1 nm with a hopping energy of 153 meV. On the other hand, within the grain, it shows a change of transport type from low temperature tunneling to beyond 300 °C as polaron hopping. The presence of disorder (defects) as the hopping sites. The temperature dependence of f res agrees with different predicted oxygen chemisorbed species between 200 °C to 400 °C. As opposed to the traditional DC response, the AC response in the imaginary part of (Z″) shows gas specific resonance frequencies for each gas, such as NO 2 , ethanol, and H 2 . Among the two reducing gases, ethanol and hydrogen; the former shows good dependence on concentration in Z″ whereas the latter shows a good response in f res as well as capacitance. Thus, the results of frequency dependent response allow us to investigate greater details of the gas sensing mechanism in ZnO, which may be exploited for selective gas sensing., (© 2023 IOP Publishing Ltd.)