Fabrication and enhanced photoluminescence properties of $$\hbox {NaLa}(\hbox {MoO}_{4})_{2}$$: $$\hbox {Sm}^{3+}$$Sm3+, $$\hbox {Bi}^{3+}$$Bi3+ phosphors with high efficiency white-light-emitting

The tetragonal scheelite-type \(\hbox {Sm}^{3+}\hbox {/Bi}^{3+}\) ions co-doped with \(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\) phosphors were synthesized by a facile sol–gel and combustion process using citric acid as complexing agent. The crystal structure and morphology of these as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore, UV-absorption and the photoluminescence (PL) properties of these phosphors were systematically investigated and the PL of the phosphors shows strong white light emissions. Efficient energy transfer from the \(\hbox {MoO}_{4}^{2-}\) group or \(\hbox {Bi}^{3+}\) ions to \(\hbox {Sm}^{3+}\) ions was established by PL investigation excited at 405 nm. The PL intensity of the studied materials was investigated as a function of different \(\hbox {Sm}^{3+}\) and \(\hbox {Bi}^{3+}\) concentrations. The PL investigations revealed that the phosphors exhibit apparent characteristic emissions, which is ascribed to the transition from the ground state energy level \(^{4}\hbox {G}_{5/2}\) to excited state energy levels \(^{6}\hbox {H}_{\mathrm{J}}\) (\(J= 5/2, 7/2, 9/2\)) and the \(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\) and \(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\), 8 mol% \(\hbox {Bi}^{3+}\) present white emissions with the CIE coordinates of (0.350, 0.285) and (0.285, 0.229), respectively. The absolute quantum efficiencies of the phosphors are 40% (\(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\)) and 52% (\(\hbox {NaLa}(\hbox {MoO}_{4})_{2}\): 4 mol% \(\hbox {Sm}^{3+}\), 8 mol% \(\hbox {Bi}^{3+}\)), respectively.     

Microwave hydrothermal synthesis and upconversion luminescence properties of $$\hbox {Yb}^{3+}$$/$$\hbox {Tm}^{3+}$$Tm3+ co-doped $$\hbox {NaY}(\hbox {MoO}_{4})_{2}$$NaY(MoO4)2 phosphor

Tetragonal \(\text {NaY}(\text {MoO}_{4})_{2}\) (NYM) phosphors co-doped with \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) ions were synthesized through microwave hydrothermal method followed by calcining treatment. Powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and photoluminescence spectra were used to characterize the properties of as-prepared samples. The results show that \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM displayed bright blue emission near 472 and 476 nm (\(^{1}\hbox {G}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition), strong near-infrared upconversion (UC) emission around 795 nm (\(^{3}\hbox {H}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition). The optimum doping concentrations of \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) for the most intense UC luminescence were obtained, and the related UC mechanism of \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM depending on pump power was studied in detail.     

Thermo-transport properties of Zn-substituted layered Li-nickel oxide, $$\hbox {LiNiO}_{2}$$

The layered Li-TM-\(\hbox {O}_{2}\) materials have been investigated extensively due to their application as cathodes in Li batteries. The electrical properties of these oxides can be tuned or controlled either by non-stoichiometry or substitution. Hence the thermo-transport properties of Zn-substituted \(\hbox {LiNi}_{1-x}\hbox {Zn}_{x}\hbox {O}_{2}\) for \(0 \le x \le 0.16\) have been investigated in the temperature range of 300–900 K for potential application as a high-temperature thermoelectric material. For \(x < 0.08\), the compounds were of single phase belonging to the space group R-3mH while for \(x > 0.08\) an additional minority phase, ZnO forms together with the main layered phase. All the compounds exhibit a semiconducting behaviour with electrical resistivity, varying in the range of  \(\sim 10^{-4}\) to \(10^{-2}\,\,\Omega \hbox {m}\) between 300 and 900 K. The electrical resistivity is found to increase with increasing Zn-substitution predominantly due to a decrease in the charge carrier hole mobility. The activation energy remains constant, \(\sim \)10  meV, with Zn-substitution. The Seebeck coefficient of the compounds is found to decrease with increasing temperature and increase with increasing Zn-substitution. The Seebeck coefficient decreases from \(\sim \)95 to \(35\ \upmu \hbox {V K}^{-1}\) and the corresponding power factor is \(\sim \)12\(\ \upmu \hbox {W m}^{-1}\ {\hbox {K}}^{-2}\) for the \(x = 0.16\) compound.     

Characterization and optical properties of $$\hbox {Pr}_{2}\hbox {O}_{3}$$-doped molybdenum lead-borate glasses

\(\hbox {Pr}^{3+}\) doped molybdenum lead-borate glasses with the chemical composition 75PbO?[25–(x \(+\) y)\(\hbox {B}_{2}\hbox {O}_{3}]\)–\(y\hbox {MoO}_{3}\)–\(x\hbox {Pr}_{2}\hbox {O}_{3}\) (where \(x = 0.5\) and 1.0 mol% and \(y = 0\) and 5 mol%) were prepared by conventional melt-quenching technique. Thermal, optical and structural analyses are carried out using DSC, UV and FTIR spectra. The physical parameters, like glass transition \((T_{\mathrm{g}})\), stability factor \((\Delta T)\), optical energy band gap \((E_{\mathrm{gopt}})\), of these glasses have been determined as a function of dopant concentration. The \({T}_{\mathrm{g}}\) and optical energy gaps of these glasses were found to be in the range of 290–350\({^{\circ }}\hbox {C}\) and 2.45–2.7 eV, respectively. Stability of the glass doped with \(\hbox {Pr}^{3+}\) is found to be moderate (\(\sim \)40). The results are discussed using the structural model of Mo–lead-borate glass.     

Synthesis and up-conversion emissions of $$\hbox {Yb}^{3+}{/}\hbox {Er}^{3+}$$, $$\hbox {Yb}^{3+}{/}\hbox {Tm}^{3+}$$Yb3+/Tm3+ and $$\hbox {Yb}^{3+}{/}\hbox {Tm}^{3+}{/}\hbox {Gd}^{3+}$$Yb3+/Tm3+/Gd3+ co-doped $$\hbox {KLu}_{2}\hbox {F}_{7}$$KLu2F7

\(\hbox {Yb}^{3+}/\hbox {Er}^{3+}\), \(\hbox {Yb}^{3+}/\hbox {Tm}^{3+}\), or \(\hbox {Yb}^{3+}/\hbox {Tm}^{3+}/\hbox {Gd}^{3+}\) co-doped \(\hbox {KLu}_{2}\hbox {F}_{7}\) up-conversion (UC) materials were synthesized through a hydrothermal method or an additive-assisted hydrothermal method. The X-ray diffraction (XRD) results suggested that the materials crystallized in orthorhombic phase, yet, the potassium citrate (CitK) introduction affected immensely the crystalline purity of final material. The field emission scanning electron microscopy (FE-SEM) results suggested that the additive adding had effects on size and morphology of the material, which affected the UC emissions further. Green/red UC emissions of \(\hbox {Er}^{3+}\), UV/blue/IR UC emissions of \(\hbox {Tm}^{3+}\), and UV UC emissions of \(\hbox {Gd}^{3+}\) were observed in the orthorhombic phase of \(\hbox {KLu}_{2}\hbox {F}_{7}\) materials. The excitation power-dependent UC emissions illustrated that the UC emission intensity initially increased, then decreased with the increase in excitation power. At the same time, the variation rates of different transitions in \(\hbox {Er}^{3+}\) or \(\hbox {Tm}^{3+}\) are also different. In addition, the \(\hbox {Er}^{3+}\) or \(\hbox {Tm}^{3+}\) concentration-dependent UC emission results suggested that the optimal doping concentration of \(\hbox {Er}^{3+}\) is 2 mol% and \(\hbox {Tm}^{3+}\) is 0.5 mol% with the \(\hbox {Yb}^{3+}\) concentration fixed as 20 mol%. The experimental results suggest that the orthorhombic phase of \(\hbox {KLu}_{2}\hbox {F}_{7}\) should be a good host lattice for UC emitters.     

Elastic and thermodynamic properties of zirconium- and hafnium-doped $$\hbox {Rh}_{3}\hbox {V}$$ intermetallic compounds: potential aerospace material

Structural, electronic, mechanical and thermodynamic properties of \(\hbox {Rh}_{3}\hbox {Zr}_{x}\hbox {V}_{1-x}\) and \(\hbox {Rh}_{3}\hbox {Hf}_{x}\hbox {V}_{1-x}\) (\(x = 0\), 0.125, 0.25, 0.75, 0.875 and 1) combinations are investigated by means of first-principles calculations based on the density functional theory within the generalized gradient approximation. Here, \(\hbox {Rh}_{3}\hbox {V}\) is chosen as the parent binary compound and the doping elements are zirconium and hafnium with the above-mentioned concentrations. The calculated lattice parameters and elastic modulus of binary \(\hbox {Rh}_{3}\hbox {Hf}\), \(\hbox {Rh}_{3}\hbox {V}\) and \(\hbox {Rh}_{3}\hbox {Zr}\) are in good agreement with the available experimental and other theoretical results. In this study, the following ternary materials viz., \(\hbox {Rh}_{3}\hbox {Zr}_{0.75}\hbox {V}_{0.25}\), \(\hbox {Rh}_{3}\hbox {Hf}_{0.25}\hbox {V}_{0.75}\) and \(\hbox {Rh}_{3}\hbox {Hf}_{0.75}\hbox {V}_{0.25}\) are found to be brittle/more brittle than the parent binary compound \(\hbox {Rh}_{3}\hbox {V}\), whereas the other ternary combinations, namely \(\hbox {Rh}_{3}\hbox {Zr}_{0.125}\hbox {V}_{0.875}\), \(\hbox {Rh}_{3}\hbox {Zr}_{0.25}\hbox {V}_{0.75}\), \(\hbox {Rh}_{3}\hbox {Zr}_{0.875}\hbox {V}_{0.125}\), \(\hbox {Rh}_{3}\hbox {Hf}_{0.125}\hbox {V}_{0.875}\) and \(\hbox {Rh}_{3}\hbox {Hf}_{0.875}\hbox {V}_{0.125}\) are found to be more ductile than \(\hbox {Rh}_{3}\hbox {V}\). The more brittle ternary combination, namely \(\hbox {Rh}_{3}\hbox {Hf}_{0.75}\hbox {V}_{0.25}\) (\(B = 229.32\,\hbox {GPa}\)) has the maximum Young’s modulus, shear modulus and hardness values; whereas the more ductile ternary \(\hbox {Rh}_{3}\hbox {Zr}_{0.25}\hbox {V}_{0.75}\) combination (\(B = 243.54\,\hbox {GPa}\)) is found to have the least values of Young’s modulus, shear modulus and hardness. The band structure, density of states histograms and charge density plots are drawn and discussed. Computed Debye temperature (\(\theta _{\mathrm{D}}\)), Grüneisen parameter (\(\zeta \)) and melting temperature (\(T_{\mathrm{m}})\) of the parent binary compound \(\hbox {Rh}_{3}\hbox {V}\), the more brittle \(\hbox {Rh}_{3}\hbox {Hf}_{0.75}\hbox {V}_{0.25}\) combination and the more ductile \(\hbox {Rh}_{3}\hbox {Zr}_{0.25}\hbox {V}_{0.75}\) combination are given by (895 K, 1.3491, 2788 K), (790 K, 1.2701, 2736 K) and (698 K, 1.7972, 2529 K), respectively.     

Distribution of relaxation times investigation of $$\hbox {Co}^{3+}$$ doping lithium-rich cathode material $$\hbox {Li}[\hbox {Li}_{0.2} \hbox {Ni}_{0.1} \hbox {Mn}_{0.5} \hbox {Co}_{0.2}]\hbox {O}_{2}$$Li[Li0.2Ni0.1Mn0.5Co0.2]O2

The element \(\hbox {Co}^{3+}\) was introduced into lithium-rich material \(0.5\hbox {Li}_{2}\hbox {MnO}_{3} \cdot 0.5 \hbox {LiNi}_{0.5}\hbox {Mn}_{0.5}\hbox {O}_{2}\) by a polyacrylamide-assisted sol–gel method to form \(\hbox {Li}[\hbox {Li}_{0.2} \hbox {Ni}_{0.1} \hbox {Mn}_{0.5} \hbox {Co}_{0.2}]\hbox {O}_{2}\) and better electro-chemical performances were observed. Electrochemical impedance spectroscopy spectra were measured on 11 specific open circuit voltage levels on the initial charge profile. Then they were converted to the distribution of relaxation times (DRTs) g(\(\tau \)) by self-consistent Tikhonov regularization method. The obtained DRTs offered a higher resolution in the frequency domain and provided the number and the physical origins of loss processes clearly. Through the analysis of DRTs, the rapid augmentation of resistance to electronic conduction and charge transfer within the voltage range 4.46–4.7 V where the removal of \(\hbox {Li}_{2}\hbox {O}\) from \(\hbox {Li}_{2} \hbox {MnO}_{3}\) component took place was the most remarkable phenomenon and the \(\hbox {Co}^{3+}\) doping greatly reduced the resistance to electronic conduction Re. This gave us more evidence about the complicated ‘structurally integrated’ composite character of the material.     

Synthesis,structure and thermoelectric properties of $$\mathrm{La}_{1-x}\mathrm{Na}_{x}\mathrm{CoO}_{3 }$$ perovskite oxides

Monovalent ion doped lanthanum cobaltate \(\hbox {La}_{1-x}\hbox {Na}_{x}\hbox {CoO}_{3 }\) (\(0 \le x \le 0.25\)) compositions were synthesized by the nitrate–citrate gel combustion method. All the heat treatments were limited to below 1123 K, in order to retain the Na stoichiometry. Structural parameters for all the compounds were confirmed by the Rietveld refinement method using powder X-ray diffraction (XRD) data and exhibit the rhombhohedral crystal structure with space group R-3c (No. 167). The scanning electron microscopy study reveals that the particles are spherical in shape and sizes, in the range of 0.2–0.5 \(\upmu \)m. High temperature electrical resistivity, Seebeck coefficient and thermal conductivity measurements were performed on the high density hot pressed pellets in the temperature range of 300–800 K, which exhibit p-type conductivity of pristine and doped compositions. The X-ray photoelectron spectroscopy (XPS) studies confirm the monotonous increase in \(\hbox {Co}^{4+}\) with doping concentration up to \(x = 0.15\), which is correlated with the electrical resistivity and Seebeck coefficient values of the samples. The highest power factor of \(10~\upmu \hbox {W~mK}^{-2 }\) is achieved for 10 at% Na content at 600 K. Thermoelectric figure of merit is estimated to be \({\sim }1 \times 10^{-2}\) at 780 K for 15 at% Na-doped samples.     

Synthesis,characterization and electrochemical performance of $$\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}$$ cathode materials for lithium ion batteries

\(\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}\) (\(x = 0\), 0.2, 0.4, 0.6, 0.8 and 1) samples were prepared by a sol–gel process. The crystal structure of prepared samples of \(\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}\) was characterized using an X-ray diffractometer. Different crystallographic parameters such as crystallite size and lattice cell parameters have been calculated. Scanning electron microscopy and Fourier transform infrared spectroscopy investigations were carried out, which reveal the morphology and function groups of the synthesized samples. Furthermore, electrochemical impedance spectra measurements are performed. The obtained results indicated that the highest conductivity is achieved for the \(\hbox {Li}_{2}\hbox {Ni}_{0.4}\hbox {Fe}_{0.6}\hbox {SiO}_{4}\) electrode compound. It was observed that Li–\(\hbox {Li}_{2}\hbox {Ni}_{0.4}\hbox {Fe}_{0.6}\hbox {SiO}_{4}\) battery has initial discharge capacity of 164 mAh \(\hbox {g}^{-1}\) at 0.1C rate. The cycle life performance of all \(\hbox {Li}_{2}\hbox {Ni}_{x}\hbox {Fe}_{1-x}\hbox {SiO}_{4}\) batteries ranged between 100 and 156 mAh \(\hbox {g}^{-1}\) with coulombic efficiency range between 70.9 and 93.9%.     

Effect of annealing temperature and $$\hbox {CdCl}_{2}$$ treatment on the photo-conversion efficiency of $$\hbox {CdTe/Zn}_{0.1}$$CdTe/Zn0.1$$\hbox {Cd}_{0.9}$$Cd0.9S thin film solar cells

We report the effects of annealing in conjunction with \(\hbox {CdCl}_{2}\) treatment on the photovoltaic properties of \(\hbox {CdTe/Zn}_{0.1}\hbox {Cd}_{0.9}\)S thin film solar cells. CdTe layer is subjected to dry \(\hbox {CdCl}_{2}\) treatment by thermal evaporation method and subsequently, heat treated in air using a tube furnace from 400 to \(500{^{\circ }}\hbox {C}\). AFM and XRD results show improved grain size and crystallographic properties of the CdTe film with dry \(\hbox {CdCl}_{2}\) treatment. This recrystallization and grain growth of the CdTe layer upon \(\hbox {CdCl}_{2}\) treatment translates into improved photo-conversion efficiencies of \(\hbox {CdTe/Zn}_{0.1}\hbox {Cd}_{0.9}\)S cell. The results of dry \(\hbox {CdCl}_{2}\) treatment were compared with conventional wet \(\hbox {CdCl}_{2}\) treatment. Photo-conversion efficiency of 5.2% is achieved for dry \(\hbox {CdCl}_{2}\)-treated cells in comparison with 2.4% of wet-treated cell at heat treatment temperature of \(425{^{\circ }}\hbox {C}\).     

Chemical synthesis and characterization of nano-sized rare-earth ruthenium pyrochlore compounds $$\hbox {Ln}_{2}\hbox {Ru}_{2}\hbox {O}_{7}$$ (Ln = rare earth)

The rare-earth ruthenium pyrochlores \(\hbox {Ln}_{2}\hbox {Ru}_{2}\hbox {O}_{7}\) (\(\hbox {Ln} = \hbox {La}^{3+}\), \(\hbox {Pr}^{3+}\), \(\hbox {Nd}^{3+}\), \(\hbox {Sm}^{3+}\) and \(\hbox {Gd}^{3+}\)) have been synthesized by the tartrate co-precipitation method, which allowed control of their composition and morphology. The preparation processes were monitored by thermal studies (TG-DTA). The obtained ruthenates were characterized by X-ray diffraction (XRD), TEM, d.c. electrical conductivity, thermoelectric power and dielectric constant measurements. X-ray diffraction patterns for all pyrochlore samples indicate a single-phase crystalline material with a cubic structure except for \(\hbox {LaRuO}_{3}\), which shows perovskite orthorhombic structure. The structural parameter for the solid obtained was successfully determined by Rietveld refinement based on the analysis of powder XRD pattern. The TEM photographs of these compounds exhibited the average particle size in the range of 36.4–73.8 nm. The data on the temperature variation of d.c. electrical conductivity showed that all rare-earth ruthanates are semiconductors and major carriers are electrons. The conduction mechanism of these compounds seems to be oxygen non-stoichiometry. The variation of dielectric constant at various frequencies showed initially interfacial polarization up to 275 kHz and beyond, which shows domain wall motion.     

Facile synthesis and characterization of rough surface $$\mathrm{V}_{2}\hbox {O}_{5}$$ nanomaterials for pseudo-supercapacitor electrode material with high capacitance

\(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials with rough surface were synthesized using commercial \(\hbox {V}_{2}\hbox {O}_{5}\), ethanol (EtOH) and \(\hbox {H}_{2}\hbox {O}\) as the starting materials by a simple hydrothermal route and combination of calcination. The electrochemical properties of \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials as electrodes in a supercapacitor device were measured using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) method. \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials exhibit the specific capacitance of 423 F \(\hbox {g}^{-1}\) at the current density of 0.5 A \(\hbox {g}^{-1}\) and retain 327 F \(\hbox {g}^{-1}\) even at the high current density of 10 A \(\hbox {g}^{-1}\). The influence of the ratio of \(\hbox {EtOH/H}_{2}\hbox {O}\), the calcined time and temperature on the morphology, purity and electrochemical property of the products is discussed in detail. The results revealed that the ratio of \(\hbox {EtOH}\hbox {/}\hbox {H}_{2}\hbox {O}= 10\hbox {/}25\) and calcination at \(400{^{\circ }}\hbox {C}\) for 2–4 h are favourable for preparing \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials and they exhibited the best electrochemical property. The novel morphology and high specific surface area are the main factors that contribute to high electrochemical performance of \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials during the charge–discharge processes. It turns out that \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials with rough surface is an ideal material for supercapacitor electrode in the present work.     

Temperature effects on the electrical characteristics of $$\mathrm{Al}/\mathrm{PTh}-\mathrm{SiO}_{2}/\mathrm{p\hbox {-}Si}$$ structure

The temperature-dependent current–voltage (\(I\text {--}V\)) and capacitance–voltage (\(C\text {--}V\)) characteristics of the fabricated Al/p-Si Schottky diodes with the polythiopene–SiO\(_{2}\) nanocomposite (\(\hbox {PTh--SiO}_{2}\)) interlayer were investigated. The ideality factor of \(\hbox {Al}/\hbox {PTh--SiO}_{2}/{p}\text {-Si}\) Schottky diodes has decreased with increasing temperature and the barrier height has increased with increasing temperature. The change in the barrier height and ideality factor values with temperature was attributed to inhomogeneties of the zero-bias barrier height. Richardson plot has exhibited curved behaviour due to temperature dependence of barrier height. The activation energy and effective Richardson constant were calculated as 0.16 eV and \(1.79 \times 10^{-8} \hbox {A\,cm}^{-2} \,\hbox {K}^{-2}\) from linear part of Richardson plots, respectively. The barrier height values determined from capacitance–voltage–temperature (\(C\text {--}V\text {--}T\)) measurements decrease with increasing temperature on the contrary of barrier height values obtained from \(I\text {--}V\text {--}T\) measurements.     

Structural and physical properties of $$\hbox {Sm}^{3+}$$ doped magnesium zinc sulfophosphate glass

Samarium (\(\hbox {Sm}^{3+})\) doped magnesium zinc sulfophosphate glass system of composition (60–\(x)\hbox {P}_{2}\hbox {O}_{5}\)–20MgO–20ZnSO\(_{4}\)–\(x\hbox {Sm}_{2}\hbox {O}_{3}\) (\(x =\) 0.0, 0.5, 1.0, 1.5 and 2.0 mol%) were synthesized using melt-quenching technique. The structure and physical properties of prepared glass samples were characterized. The X-ray diffraction pattern verified their amorphous nature. The physical properties such as density, refractive index, molar volume, rare earth ion concentration, etc. were calculated. The decrease in the optical bandgap energy with increasing \(\hbox {Sm}_{2}\hbox {O}_{3}\) contents was attributed to the alteration in the glass network structures. Fourier transformed infrared spectra and Raman analyses manifested the depolymerization of \(\hbox {ZnSO}_{4}\) in the phosphate host matrix. The present findings may be beneficial for the advancement of functional glasses.     

Resistance-switching properties of Bi-doped $$\hbox {SrTiO}_{3}$$ films for non-volatile memory applications with different device structures

\(\hbox {SrTiO}_{3}\) and Bi-doped \(\hbox {SrTiO}_{3}\) films were fabricated with different device structures using the sol–gel method for non-volatile memory applications, and their resistance-switching behaviour, endurance and retention characteristics were investigated. \(\hbox {SrTiO}_{3}\) and \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si or Pt have the same phase structure, morphologies and grain size; however, the grain size of the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si is slightly larger than those of the \(\hbox {SrTiO}_{3}\) films grown on Si and the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Pt. The \(\hbox {SrTiO}_{3}\) or \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si or Pt all exhibit bipolar resistive-switching behaviour and follow the same conductive mechanism; however, the \(\hbox {Ag}/\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}/\hbox {Si}\) device possesses the highest \(R_{\mathrm{HRS}}{/}R_{\mathrm{LRS}}\) of \(10^{5}\) and the best endurance and retention characteristics. The doping of Bi is conducive to enhance the \(R_{\mathrm{HRS}}{/}R_{\mathrm{LRS}}\) of the \(\hbox {SrTiO}_{3}\) films; meanwhile, the Si substrates help improve the endurance and retention characteristics of the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films.     

High-pressure studies of superconductivity in $$\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}$$

\(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\) crystallizes in tetragonal CeOBiS\(_{2}\) structure (S. G. P4/nmm). We have investigated the effect of pressure on magnetization measurements. Our studies suggest improved superconducting properties in polycrystalline samples of \(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\). The \(T_{\mathrm{c}}\) in our sample is 5.3 K, at ambient pressure, which is marginal but definite enhancement over \(T_{\mathrm{c}}\) reported earlier (= 5.1 K). The upper critical field \(H_{\mathrm{c}2}\)(0) is greater than 3 T, which is higher than earlier report on this material. As determined from the M–H curve, both \(H_{\mathrm{c}2}\) and \(H_{\mathrm{c}1}\) decrease under external pressure P (0 \(\le P \le \) 1 GPa). We observe a decrease in critical current density and transition temperature on applying pressure in \(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\).     

Role of reactive species in the photocatalytic degradation of amaranth by highly active N-doped $$\mathbf{WO}_{\mathbf{3}}$$

A novel, highly visible light active N-doped \(\hbox {WO}_{3}\) (\(\hbox {N}\)-\(\hbox {WO}_{3})\) is successfully synthesized via thermal decomposition of peroxotungstic acid–urea complex. The photocatalytic activity of \(\hbox {N}\)-\(\hbox {WO}_{3}\) is evaluated for the degradation of amaranth (AM) dye under visible and UVA light along with the role of reactive species, which has not yet been studied for \(\hbox {N}\)-\(\hbox {WO}_{3}\) photocatalysts. Doping of N into substitutional and interstitial sites of \(\hbox {WO}_{3}\) is confirmed by X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy. At a pH of 7, 1 g \(\hbox {l}^{-1}\) of \(\hbox {N}\)-\(\hbox {WO}_{3}\) can completely degrade \(10\,\hbox {mg } \hbox {l}^{-1}\) of AM within 1 h under visible and UVA light. For the degradation of AM by \(\hbox {N}\)-\(\hbox {WO}_{3}\) under visible and UVA light, \(\hbox {h}^{+}\) is found to be the main reactive species, while \(\cdot \hbox {OH}\) contributes to a lesser extent. On the contrary, \(^{1}\hbox {O}_{2}, \cdot \hbox {O}_{2}^{-}\) and \(\hbox {e}^{-}\) show negligible roles. The crucial role of \(\hbox {h}^{+}\) indicates effective suppression of electron–hole recombination after N doping. Dye sensitization and oxidation by reactive species are found to be the major pathway for the degradation of AM under visible and UVA light, respectively.     

A first-principle investigation into effect of B- and BN-doped $$\hbox {C}_{60}$$ in lowering dehydrogenation of $$\hbox {MXH}_{4}$$MXH4 (where M $$=$$= Na,Li and X $$=$$= Al,B)

The present paper reports the effect of B- and BN-doped \(\hbox {C}_{60}\) as catalysts for lowering the dehydrogenation energy in \(\hbox {MXH}_{4}\) clusters (M = Na and Li, X = Al and B) using density functional calculations. \(\hbox {MXH}_{4}\) interacts strongly with B-doped \(\hbox {C}_{60}\) and weakly with BN-doped \(\hbox {C}_{60}\) in comparison with pure \(\hbox {C}_{60}\) with binding energy 0.56–0.80 and 0.05–0.34 eV, respectively. The hydrogen release energy \((E_{\mathrm{HRE}})\) of \(\hbox {MXH}_{4}\) decreases sharply in the range of 38–49% when adsorbed on B-doped \(\hbox {C}_{60}\); however, with BN-doped \(\hbox {C}_{60}\) the decrease in the \(E_{\mathrm{HRE}}\) varies in the range of 6–20% as compared with pure \(\hbox {MXH}_{4}\) clusters. The hydrogen release energy of second hydrogen atom in \(\hbox {MXH}_{4}\) decreases sharply in the range of 1.7–41% for BN-doped \(\hbox {C}_{60}\) and decreases in the range of 0.2–11.3% for B-doped \(\hbox {C}_{60}\) as compared with pure \(\hbox {MXH}_{4}\) clusters. The results can be explained on the basis of charge transfer within \(\hbox {MXH}_{4}\) cluster and with the doped \(\hbox {C}_{60}\).     

Influence of $$\hbox {TiO}_{2}$$ particle size and conductivity of the CuCrO$$_{2}$$2 nanoparticles on the performance of solid-state dye-sensitized solar cells

Solid-state dye-sensitized solar cells have been fabricated with mesoporous \(\hbox {TiO}_{2 }\) photoanode and N719 dye as photosensitizer. First, \(\hbox {TiO}_{2}\) and non-doped, Zn- and Mg-doped CuCrO\(_{2}\) nanoparticles have been synthesized by sol–gel method. In addition, the \(\hbox {TiO}_{2}\) pastes have been prepared through Pechini-type sol–gel method. The effect of \(\hbox {TiO}_{2}\) particle size, mesoporous \(\hbox {TiO}_{2}\) photoanode thickness and solid-state electrolyte thickness on the efficiency of the fabricated devices has been investigated. Our results show that in spite of the low amount of dye loading for photoanode with large \(\hbox {TiO}_{2}\) nanoparticles (80–180 nm), the dye-sensitized solar cell made from it has higher efficiency than that constructed from the photoanode comprising of small particles about 10–15 nm in size. The higher efficiency is attributed to the longer diffusion length of electrons because of a better electron transport and penetration of a large amount of \(\hbox {CuCrO}_{2 }\) nanoparticles in the porous structure of \(\hbox {TiO}_{2}\) photoanode. By using the doped \(\hbox {CuCrO}_{2}\) nanoparticles, the efficiency has been increased from 0.027% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\) to 0.033% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Zn and further increased to 0.042% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Mg. The efficiency enhancement by doping is ascribed to the conductivity improvement due to the presence of impurity atoms.     

Evaluation of the elastic properties of monovalent oxides using $$\hbox {TeO}_{2}$$-based glasses

Quaternary tellurite glasses with composition \(75\hbox {TeO}_{2}\)–\(5\hbox {WO}_{3}\)–\(15\hbox {Nb}_{2} \hbox {O}_{5}\)–\(5\hbox {M}_{x} \hbox {O}_{y}\) in mol%, where \(\hbox {M}_{x}\hbox {O}_{y}\) = (\(\hbox {Na}_{2}\hbox {O}, \, \hbox {Ag}_{2}\hbox {O}\), ZnO, MgO, CuO, NiO, \(\hbox {TiO}_{2}\), \(\hbox {MnO}_{2}\)), were prepared by the normal melt-quenching method. The ultrasonic velocities (longitudinal and shear) were measured in these glasses using the pulse-echo technique at room temperature. Their elastic moduli, microhardness and Debye temperature were calculated and discussed in terms of the modifier’s ionicity and quantitatively in terms of number of bonds per unit volume and the cross-link density. In this study, the values of ultrasonic velocities, elastic moduli, Debye temperature and microhardness were found to be strongly dependent on three factors, namely: (i) modifier’s ionicity; (ii) trigonal pyramid (\(\hbox {TeO}_{3}\))/trigonal bipyramid (\(\hbox {TeO}_{4}\)) ratio; and (iii) glass transition temperature \(T_\mathrm{g}\). We used the Makishima and Mackenzie’s model to calculate the theoretical elastic moduli and to indicate that the experimental values were in good agreement with the theoretical values.