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.     

Superconducting epitaxial $$\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\delta }$$ on $$\hbox {SrTiO}_{3}$$SrTiO3-buffered Si(001)

Thin films of optimally doped(001)-oriented \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) are epitaxially integrated on silicon(001) through growth on a single crystalline \(\hbox {SrTiO}_{3}\) buffer. The former is grown using pulsed-laser deposition and the latter is grown on Si using oxide molecular beam epitaxy. The single crystal nature of the \(\hbox {SrTiO}_{3}\) buffer enables high quality \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) films exhibiting high transition temperatures to be integrated on Si. For a 30-nm thick \(\hbox {SrTiO}_{3}\) buffer, 50-nm thick \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) films that exhibit a transition temperature of \(\sim \)93 K, and a narrow transition width (<5 K) are achieved. The integration of single crystalline \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\updelta }\) on Si(001) paves the way for the potential exploration of cuprate materials in a variety of applications.     

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.     

Influence of Thermal Annealings in Argon on the Structural and Thermochromic Properties of $$\mathrm{MoO}_{3}$$ Thin Films

The effect of thermal annealing in an inert atmosphere (argon) on the structural and thermochromic properties of \(\hbox {MoO}_{3}\) thin films was investigated. \(\hbox {MoO}_{3}\) thin films were deposited by thermal evaporation in vacuum of \(\hbox {MoO}_{3}\) powders. X-ray diffraction patterns of the films showed the presence of the monoclinic Magneli phase \(\hbox {Mo}_{9}\hbox {O}_{26}\) for annealing temperatures above \(250\,{^{\circ }}\hbox {C}\). Absorbance spectra of the films annealed in argon indicated that their thermochromic response increases with the annealing temperature in the analyzed range (23 \({^{\circ }}\hbox {C}\)–300 \({^{\circ }}\hbox {C}\)), a result opposite to the case of thermal annealings in air, for which case the thermochromic response shows a maximum value around 200 \({^{\circ }}\)C–225 \({^{\circ }}\)C and decreases for higher temperatures. These results are explained in terms of a higher density of oxygen vacancies formed upon thermal treatments in inert atmospheres.     

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.     

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.     

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 \(\hbox {BiO}_{0.75}\hbox {F}_{0.25}\hbox {BiS}_{2}\).     

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 \(\hbox {C}_{60}\).     

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.     

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%.     

Radiative Properties of Ceramic $$\hbox {Al}_{2}\hbox {O}_{3}$$, AlN,and $$\hbox {Si}_{3}\hbox {N}_{4}$$Si3N4: I. Experiments

The radiative properties of dense ceramic \(\hbox {Al}_{2}\hbox {O}_{3}\), AlN, and \(\hbox {Si}_{3}\hbox {N}_{4}\) plates are investigated from the visible to the mid-infrared region at room temperature. Each specimen has different surface finishings on different sides of the laminate. A monochromator was used with an integrating sphere to measure the directional-hemispherical reflectance and transmittance of these samples at wavelengths from 0.4 \(\upmu \hbox {m}\) to 1.8 \(\upmu \hbox {m}\). The specular reflectance was obtained by a subtraction technique. A Fourier-transform infrared spectrometer was used to measure the directional-hemispherical or specular reflectance and transmittance with appropriate accessories from about 1.6 \(\upmu \hbox {m}\) to 19 \(\upmu \hbox {m}\). All measurements were performed at near-normal incidence on either the smooth side or the rough side of the sample. The experimental observations are qualitatively interpreted considering the optical constants, surface roughness, and volume scattering and absorption.     

Influence of the conditions of a solid-state synthesis anode material $$\hbox {Li}_{4}\hbox {Ti}_{5}\hbox {O}_{12 }$$ on its electrochemical properties of lithium cells

Lithium–titanium spinel is a promising electrode material for high power and environmentally friendly batteries. We did research on \(\hbox {Li}_{4}\hbox {Ti}_{5}\hbox {O}_{12 }\) (LTO) samples, which were synthesized via solid-state reaction at various conditions in a temperature range from 800 to \(900{^{\circ }}\hbox {C}\) and they were investigated by XRD, SEM, IS, cyclic voltammetry and the galvanostatic charge–discharge tests. X-ray diffractions show that all of the samples have a spinel structure with Fd-3m space group with a small amount of impurities \(\hbox {TiO}_{2}\) (anatase). Lithium ion batteries with LTO-based electrode exhibit excellent reversible capacity of \(\,\sim 180\hbox { mAh}\hbox { g}^{-1}\) in the current density range from 0.1 to 1 C. As an electrode material for rechargeable lithium-ion batteries, LTO-F demonstrates the best rate and cyclic performance from all of the studied samples.     

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.     

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.     

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.     

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.     

Effect of annealing treatment on optical properties and microstructural variation of $$\hbox {WO}_{3}/\hbox {Ag}/\hbox {WO}_{3}$$ multilayer nano-films

Structural and optical properties of \(\text {WO}_{3}/\text {Ag}/\text {WO}_{3}\) nano-multilayer composites were investigated for heat mirror applications. \(\text {WO}_{3}/\text {Ag}/\text {WO}_{3}\) thin films were fabricated through a physical vapour deposition method by using electron-beam evaporation at the vacuum chamber at 10\(^{-5}\) Torr. \(\text {WO}_{3}\) nano-layer was fabricated at 40 nm. Annealing treatment was carried out at 100, 200, 300 and 400\(^{\circ }\)C for 1 h after the deposition of first layer of \(\text {WO}_{3}\) on the glass. On \(\text {WO}_{3}\) film, Ag nano-layers with 10, 12 or 14 nm thickness were deposited. Individual layers morphology was investigated using atomic force microscopy (AFM) and deduced that a smoother layer can be achieved after the annealing at 300\(^{\circ }\)C. Ellipsometry analysis was executed to determine both layers, Ag film thickness and inter-diffusion between the \(\text {WO}_{3}\)–Ag–\(\text {WO}_{3}\) layers. It was inferred that there was almost no interfering among the \(\text {WO}_{3}\)–\(\text {WO}_{3 }\) layers in the samples with 12 and 14 nm Ag thickness; while silver was deposited on the annealed \(\text {WO}_{3}\) layer at 300\(^{\circ }\)C. UV–visible spectrophotometer showed that the annealing treatment of the first \(\text {WO}_{3}\) layer enhanced the transparency of films in the visible region. The innovations of the present study have been based on the annealing of the films and finding an optimum thickness for the Ag film at 12–14 nm. Heat mirrors efficiency was assessed according to the principle of their optical behaviour and optimum performance obtained for 14 nm of Ag film, deposited on annealed tungsten oxide at 300\(^{\circ }\)C.     

Evaluation of Thermodynamic Models for Predicting Phase Equilibria of $$\hbox {CO}_{2}$$ + Impurity Binary Mixture

For the design and operation of \(\hbox {CO}_{2}\) capture and storage (CCS) processes, equation of state (EoS) models are used for phase equilibrium calculations. Reliability of an EoS model plays a crucial role, and many variations of EoS models have been reported and continue to be published. The prediction of phase equilibria for \(\hbox {CO}_{2}\) mixtures containing \(\hbox {SO}_{2}\), \(\hbox {N}_{2}\), NO, \(\hbox {H}_{2}\), \(\hbox {O}_{2}\), \(\hbox {CH}_{4}\), \(\hbox {H}_{2}\mathrm{S}\), Ar, and \(\hbox {H}_{2}\mathrm{O}\) is important for \(\hbox {CO}_{2}\) transportation because the captured gas normally contains small amounts of impurities even though it is purified in advance. For the design of pipelines in deep sea or arctic conditions, flow assurance and safety are considered priority issues, and highly reliable calculations are required. In this work, predictive Soave–Redlich–Kwong, cubic plus association, Groupe Européen de Recherches Gazières (GERG-2008), perturbed-chain statistical associating fluid theory, and non-random lattice fluids hydrogen bond EoS models were compared regarding performance in calculating phase equilibria of \(\hbox {CO}_{2}\)-impurity binary mixtures and with the collected literature data. No single EoS could cover the entire range of systems considered in this study. Weaknesses and strong points of each EoS model were analyzed, and recommendations are given as guidelines for safe design and operation of CCS processes.     

Structural,dielectric and piezoelectric study of Ca-, Zr-modified $$\hbox {BaTiO}_{3}$$ lead-free ceramics

We prepared a lead-free ceramic (\(\hbox {Ba}_{0.85}\hbox {Ca}_{0.15})(\hbox {Ti}_{1-x}\hbox {Zr}_{x})\hbox {O}_{3}\) (BCTZ) using the conventional mixed oxide technique. The samples were prepared by an ordinary mixing and sintering technique. In this study we investigated how small amounts of \(\hbox {Zr}^{4+}\) can affect the crystal structure and microstructure as well as dielectric and piezoelectric properties of \(\hbox {BaTiO}_{3}\). X-ray diffraction analysis results indicate that no secondary phase is formed in any of the BCTZ powders for \(0 \le x \le 0.1\), suggesting that \(\hbox {Zr}^{4+}\) diffuses into \(\hbox {BaTiO}_{3}\) lattices to form a solid solution. Scanning electron microscopy micrographs revealed that the average grain size gradually increased with \(\hbox {Zr}^{4+}\) content from 9.5 \(\upmu \!\hbox {m}\) for \(x = 0.02\) to 13.5 \(\upmu \!\hbox {m}\) for \(x = 0.1\); Curie temperature decreased due to the small tetragonality caused by \(\hbox {Zr}^{4+}\) addition. Owing to the polymorphic phase transition from orthorhombic to tetragonal phase around room temperature, it was found that the composition \(x = 0.09\) showed improved electrical properties and reached preferred values of \(d_{33} = 148\) pC \(\hbox {N}^{-1}\) and \(K_{\mathrm{p}} = 27\%\).     

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.