arXiv subjects

Ambesh Dixit

Publications and source records attributed to Ambesh Dixit.

27 records · Page 2Linked to original sources

arXiv2018

Inverted structure perovskite solar cells: A theoretical study

We analysed perovskite CH3NH3PbI3-xClx inverted planner structure solar cell with nickel oxide (NiO) and spiro-MeOTAD as hole conductors. This structure is free from electron transport layer. The thickness is optimized for NiO and spiro-MeOTAD hole conducting materials and the devices do not exhibit any significant variation for both hole transport materials. The back metal contact work function is varied for NiO hole conductor and observed that Ni and Co metals may be suitable back contacts for efficient carrier dynamics. The solar photovoltaic performance showed a linear decrease in efficiency with increasing temperature. The electron affinity and band gap of transparent conducting oxide and NiO layers are varied to understand their impact on conduction and valence band offsets. A range of suitable band gap and electron affinity values are found essential for efficient device performance.

physics.app-ph↗

arXiv2018

Simulation studies of CZT(S,Se) single and tandem junction solar cells towards possibilities for higher efficiencies up to 22%

We simulated photovoltaic characteristics of single heterojunction solar cell with Cu2ZnSnS4 and Cu2ZnSnSe4 absorber layer numerically using one dimensional solar cell capacitance simulator (SCAPS-1D). n-CdS/ZnO double buffer layer is used for hetrostructure interfaces with the absorber layer. The cell performance is investigated against variation of different material layer properties such as thickness, carrier concentration, defect density etc. The performance is optimized first for the single junction solar cell with Mo as back contact material with work function 5 eV. A double junction CZTS/CZTSe tandem cell structure is realized keeping the same material properties as is used in the single CZTS and CZTSe solar cell simulation and considering the flat band condition at the interface. Tandem cell performance is determined after matching the current condition for top and bottom sub-cells. The CZTS/CZTSe short circuit current density is ~ 20.98 mA/cm2 for current matched 211.33 nm thick CZTS top cell in conjunction with 2000 nm bottom cell. The maximum efficiency obtained under the flat band condition at the contact is ~21.7% with open circuit voltage ~1.324 V.

physics.app-ph↗

arXiv2018

Non-volatile bipolar resistive switching in sol-gel derived BiFeO3 thin films

BiFeO3 thin films are deposited on FTO coated glass substrates using a simple sol-gel deposition technique, limiting thickness about 70 nm and Ag/BiFeO3/FTO RRAM devices are prepared. The devices showed low-voltage bipolar switching with the maximum Ion/Ioff ~ 450, and low set and reset voltages ~ 1.1 V and -1.5 V, respectively. The devices are stable against on-off cycles with ~ 104 s retention time without any significant degradation. The variations in the set and reset voltages are 0.4 V and 0.6 V, respectively. We found that ohmic and trap-controlled space charge limited conductions are responsible for low and high resistance states, respectively. The resistive switching mechanism is attributed to the formation and rupturing of the metal filament during the oxidation and reduction of Ag ions for the set and reset states.

cond-mat.mtrl-sci↗

arXiv2017

Cation modified A2(Ba, Sr, and Ca)ZnWO6 cubic double perovskites: A theoretical study

The cubic double perovskites A2ZnWO6 (A = Ba, Sr and Ca) are studied to understand the effect of A cation site, using the density functional theory (DFT) based full potential augmented plane wave method (FP-LAPW) with GGA and mBJ exchange correlation potentials. The structural robustness and stability are investigated using the bond lengths and the total energy. The band structure and density of states suggest that all these cubic double perovskites are indirect wide band gap semiconductors. The band gap varies from 3.90 eV (2.97 eV) for Ba2ZnWO6 system to 3.40 eV (2.8 eV) for Ca2ZnWO6 system using mBJ (GGA) exchange correlation potentials. Our studies suggest that cation site modification has a strong effect on physical and electronic properties, in contrast to the structural robustness. The lattice parameter decreases from 8.19 Angstrom to 7.9 Angstrom from Ba to Ca at alkali cation site and the electronic band gap variation follows the common cation rule. The charge densities show enhanced localization of charges near the zinc and oxygen sites with increasing alkali cation atomic radii. In addition, we discuss the impact of A site cation modification on the dielectric and optical properties for A2ZnWO6 double perovskites.

cond-mat.mtrl-sci↗

arXiv2017

Transition metal doped ZnS monolayer: The first principles insights

Structural and electronic properties of pristine and transition metal doped ZnS monolayer are investigated within the framework of density functional theory. The pristine ZnS monolayer is showing direct band gap of about 2.8 eV. The investigated transition metal doping showed the transition from non-magnetic semiconductor to a magnetic system e.g. magnetic semiconductor for Co doped ZnS and half metal for Ni doped ZnS monolayers. The Co doped ZnS monolayer showed higher formation energy, confirming the strong bonding than that of Ni doped ZnS monolayer. The electron difference density shows the charge sharing between transition metal (Ni and Co) and S, confirming the covalent bond formation.

cond-mat.mtrl-sci↗

arXiv2016

Influence of Ni doping on critical parameters of PdTe superconductor

We report the effect of Ni doping on superconductivity of PdTe. The superconducting parameters like critical temperature (Tc), upper critical field (Hc2) and normalized specific-heat jump are reported for Ni doped Pd1-xNixTe. The samples of series Pd1-xNixTe with nominal compositions x=0, 0.01, 0.05, 0.07, 0.1, 0.15, 0.2, 0.3 and 1.0 are synthesized via vacuum shield solid state reaction route. All the studied samples of Pd1-xNixTe series are crystallized in hexagonal crystal structure as refined by Rietveld method to space group P63/mmc. Both the electrical resistivity and magnetic measurements revealed that Tc decreases with increase of Ni concentration in Pd1-xNixTe. The magneto-transport measurements suggest that flux is better pinned for 20% Ni doped PdTe as compared to other compositions of Pd1-xNixTe. The effect and contribution of Ni 3d electron to electronic structure and density of states near Fermi level in Pd1-xNixTe are also studied using first-principle calculations within spin polarized local density approximation. The overlap of bands at Fermi level for NiTe is larger as compared to PdTe. Also the density of states just below Fermi level (in conduction band) drops much lower for PdTe than as for NiTe. Summarily, Ni doping in Pd1-xNixTe superconductor suppresses superconductivity moderately and also Ni is of non magnetic character in these compounds.

cond-mat.supr-con↗

arXiv2015

beta phase manganese dioxide nanorods Synthesis and characterization for supercapacitor applications

Manganese dioxide nanorods were synthesized using novel solution route. The phase and microstructure of synthesized materials were identified using X ray diffraction, scanning electron and transmission electron microscopic measurements. The material crystallizes into beta crystallographic phase and consists of nanorods of diameter in the range of about 10-14 nm and length about 50 nm. The Fourier Transform Infrared (FTIR) spectroscopic and thermogravimetric analysis (TGA) measurements were carried out to understand the materials microscopic and thermal properties. The material exhibits characteristic Mn O vibrational frequencies, confirming the phase purity of material. The electrochemical performance of beta MnO2 nanorods was evaluated using cyclic voltammetry and galvanostatic charge and discharge measurements using inhouse developed supercapacitor device assembly. We observed about 125 F per g specific capacitance for beta MnO2 nanorods electrode materials.

cond-mat.mtrl-sci↗

arXiv2015

PdTe a 4.5K Type II BCS Superconductor

We report on the structure and physical properties of bulk Palladium Tellurium superconductor, which is synthesized via quartz vacuum encapsulation technique at 750 C. The as synthesized compound is crystallized in hexagonal crystal structure. Magnetization and Magneto-transport measurements provided the values of lower and upper critical field to be 250 and 1200 Gauss respectively at 2 Kelvin. The Coherence length and GL parameter are estimated from the experimentally determined upper and lower critical fields, which are 45 nm and 1.48 respectively. The jump in Cp(T) at Tc is found to be 1.33 and the Debye temperature and electronic specific heat constant are 203 Kelvin and 6.01mJ/mole-K2 respectively.

cond-mat.supr-con↗

arXiv2009

Magnetic Structure and Susceptibility of CoSe$_2$O$_5$: A Low Dimensional Antiferromagnet

CoSe$_2$O$_5$ has a crystal structure consisting of zig-zag chains of edge shared CoO$_6$ octahedra running along the c axis, with the chains separated by Se$_2$O$_5^{2-}$ units. Magnetic susceptibility measurements indicate a transition at 8.5 K to an ordered state. We investigate here the nature of this magnetic ordering using magnetization and specific heat measurements in addition to powder neuttron diffraction. A transition to long-range antiferromagnetic order is found below $T_N$ = 8.5 K as identified by magnetic susceptibility measurements and magnetic Bragg reflections, with a propagation vector $\mathbf{k}$ = 0. The magnetic structure shows that the moments align perpendicular to the c-axis, but with the spins canting with respect to the a axis by, alternately, $+8^\circ$ and $-8^\circ$. Interestingly, the low-field magnetic susceptibility does not show the anticipated cusp-like behavior expected for a well-ordered antiferromagnet. When the susceptibility is acquired under field-cooling conditions under a 10 kOe field, the the usual downturn expected for antiferromagnetic ordering is obtained. Heat capacity measurements at low temperatures indicate the presence of gapped behavior with a gap of 6.5 K.

cond-mat.mtrl-sci↗