Properties of Ni1−xFex (0.1 < x < 0.9) and Invar (x = 0.64) alloys obtained by electrodeposition

Electrodeposition of Ni_1−xFe_x (x = 0.1-0.9) films was carried out from a chloride plating solution containing saccharin as an organic additive at a constant current density (5 mA/cm²) and a controlled pH of 2.5. X-ray diffraction studies revealed the existence of an fcc, or γ phase, in the range of 10-58 wt.% Fe, a mixed fcc/bcc phase in the range of 59-60 wt.% Fe, and a bcc, or α phase in the range of 64-90 wt.% Fe. The saturation magnetization, B_s, of electrodeposited Ni_1−xFe_x alloys at the room temperature was found to increase with the increase of Fe-content and follows the Slater-Pauling curve, but deviates from as-cast bulk NiFe alloys. The coefficient of thermal expansion, CTE, of electrodeposited alloys at room temperature also deviates from as-cast bulk NiFe alloys. Annealing of α-Ni₃₆Fe₆₄ alloy results in a martensitic α → γ phase transformation, which takes place between 300 and 400 °C. It was demonstrated that thermal treatment above 400 °C was necessary to obtain magnetic and mechanical properties similar to those to conventional Invar alloy. Annealing of α-Ni₃₆Fe₆₄ alloy at 700 °C brings about a decrease of B_s from 1.75 to 0.45 T. By controlling the annealing conditions of α → γ martensitic transformation, it is possible to adjust the CTE of Ni₃₆Fe₆₄ alloy over the broad limits from 2.7 to 8.7 × 10⁻⁶/°C.     

FexCo0.5−xNi0.5-SDC anodes for low-temperature solid oxide fuel cells

Trimetal alloys, Fe_xCo_0.5−xNi_0.5 (x = 0.1, 0.2, 0.25, 0.3, 0.4), were studied as anodes for low-temperature solid oxide fuel cells (LT-SOFCs) based on GDC (Ce_0.9Gd_0.1O_1.95) electrolytes. The alloys were formed by in situ reduction of Fe_xCo_0.5−xNi_0.5O_y composites, which were synthesized using a glycine-nitrate technique. Symmetrical cells consisted of Fe_xCo_0.5−xNi_0.5-SDC electrodes and GDC electrolytes, and single cells consisted of Fe_xCo_0.5−xNi_0.5-SDC (Ce_0.8Sm_0.2O_1.9) anodes, GDC electrolytes, and SSC (Sm_0.5Sr_0.5CoO₃)-SDC cathodes were prepared using a co-pressing and co-firing process. Interfacial polarization resistances and I-V curves of these cells were measured at temperature from 450 to 600 °C. With Fe_0.25Co_0.25Ni_0.5-SDC as anodes, the cells showed the lowest interfacial resistance and highest power density. For example, at 600 °C, the resistance was about 0.11 Ω cm² and power density was about 750 mW cm⁻² when humidified (3% H₂O) hydrogen was used as fuel and stationary air as oxidant. Further, the cell performance was improved when the molar ratio of Fe:Co:Ni approached 1:1:2, i.e. Fe_0.25Co_0.25Ni_0.5. In addition, higher power density and lower interfacial resistance were obtained for cells with the Fe_0.25Co_0.25Ni_0.5-SDC anodes comparing to that with Ni-SDC anodes, which have been usually used for LT-SOFCs. The promising performance of Fe_xCo_0.5−xNi_0.5 as anodes suggests that trimetallic anodes are worth considering for SOFCs that operate at low-temperature.     

Structure,magnetic and electrical transport properties of the perovskites Sm1−xCaxFe1−xMnxO3

The structure of series Sm_1−xCa_xFe_1−xMn_xO₃ (0.0 ≤ x ≤ 1.0) compounds was investigated. The lattice parameters increase with coupled substitution Sm³⁺ by Ca²⁺ and Mn⁴⁺ for Fe³⁺. The variation of parameter, c, is larger than that of a and b, respectivly. The detailed analysis of magnetic properties of series Sm_1−xCa_xFe_1−xMn_xO₃ (0.1 ≤ x ≤ 0.9) shows that local magnetic interaction between Fe³⁺ and Fe³⁺ and Mn⁴⁺ and Mn⁴⁺ at below magnetic transition temperature is antiferromagnetic. Above magnetic transition temperature the presence of large magnetic cluster is proposed and the sizes of magnetic clusters decrease with Mn⁴⁺. The electrical transport behaviors related with small polaron hopping and variable range hopping models.     

Quantitative study of pH change during LaNi5−xAlx (x = 0, 0.3) discharge process by SECM

Oxygen reduction reaction (ORR) on Pt microelectrode was used for developing a micro pH sensor for scanning electrochemical microscopy (SECM) study in this work. When the potential of Pt microelectrode was held constant in ORR region, the ORR current (cathodic current) increased with decreasing solution pH and vice versa. The response time of the ORR current to pH changes was measured to be ca. 30 ms which implies that the pH response is fast enough for monitoring the temporal pH changes. Furthermore, a fine linear relationship was found to exist between the half wave potential of ORR (E_1/2) and the solution pH value, and the slope is −46 mV/pH. The Pt micro pH sensor was located 1 μm above the LaNi_5−xAl_x (x = 0, 0.3) substrate electrode surface in pH = 9 KOH solution to perform the tip-substrate voltammetry of SECM. In tip voltammogram, the ORR tip current qualitatively reflects the transit solution pH changes during LaNi_5−xAl_x discharge reaction. Also, the minimum values of the solution pH near LaNi₅ and LaNi_4.7Al_0.3 surface during the discharge reaction were quantitatively detected; they were 7.17 and 7.57, respectively. The result indicates that Al partial substitution for Ni degrades the maximum discharge ability of the alloy and decreases the hydrogen diffusion coefficient in alloy bulk.     

On the spinel formation in Co1 − xO/Co2TiO4 composites via reactive sintering, exsolution and oxidation

The formation mechanism and microstructural development of the spinel phases in the Co_1 − xO/Co₂TiO₄ composites upon reactive sintering the Co_1 − xO and TiO₂ powders (9:1 molar ratio) at 1450 °C and during subsequent cooling in air were studied by X-ray diffraction and analytical electron microscopy. The Co₂TiO₄ spinel occurred as inter- and intragranular particles in the matrix of Ti-doped Co_1 − xO grains with a rock salt-type structure during reactive sintering. The submicron sized Co₂TiO₄ particles were able to detach from grain boundaries in order to reach an energetically favorable parallel orientation with respect to the host Co_1 − xO grains via a Brownian-type rotation/coalescence process. Upon cooling in air, secondary Co₂TiO₄ nanoparticles were precipitated and the Ti-doped Co_1 − xO host was partially oxidized as Co_3 − δO₄ spinel by rapid diffusion along the {1 1 1} and {1 0 0}-decorated interphase interface and the free surface of the composites.     

Effect of La/Ce ratio on the structure and electrochemical characteristics of La0.7−xCexMg0.3Ni2.8Co0.5 (x = 0.1-0.5) hydrogen storage alloys

The effect of La/Ce ratio on the structure and electrochemical characteristics of the La_0.7−xCe_xMg_0.3Ni_2.8Co_0.5 (x = 0.1, 0.2, 0.3, 0.4, 0.5) alloys has been studied systematically. The result of the Rietveld analyses shows that, except for small amount of impurity phases including LaNi and LaNi₂, all these alloys mainly consist of two phases: the La(La, Mg)₂Ni₉ phase with the rhombohedral PuNi₃-type structure and the LaNi₅ phase with the hexagonal CaCu₅-type structure. The abundance of the La(La, Mg)₂Ni₉ phase decreases with increasing cerium content whereas the LaNi₅ phase increases with increasing Ce content, moreover, both the a and cell volumes of the two phases decrease with the increase of Ce content. The maximum discharge capacity decreases from 367.5 mAh g⁻¹ (x = 0.1) to 68.3 mAh g⁻¹ (x = 0.5) but the cycling life gradually improve. As the discharge current density is 1200 mA g⁻¹, the HRD increases from 55.4% (x = 0.1) to 67.5% (x = 0.3) and then decreases to 52.1% (x = 0.5). The cell volume reduction with increasing x is detrimental to hydrogen diffusion D and accordingly decreases the low temperature dischargeability of the La_0.7−xCe_xMg_0.3Ni_2.8Co_0.5 (x = 0.1-0.5) alloy electrodes.     

Electrochemical properties of La1−xSrxFeO3 (x = 0.2, 0.4) as negative electrode of Ni-MH batteries

La_(1−x)Sr_xFeO₃ (x = 0.2,0.4) powders were prepared by a stearic acid combustion method, and their phase structure and electrochemical properties were investigated systematically. X-ray diffraction (XRD) analysis shows that La_(1−x)Sr_xFeO₃ perovskite-type oxides consist of single-phase orthorhombic structure (x = 0.2) and rhombohedral one (x = 0.4), respectively. The electrochemical test shows that the reaction at La_(1−x)Sr_xFeO₃ oxide electrodes are reversible. The discharge capacities of La_(1−x)Sr_xFeO₃ oxide electrodes increase as the temperature rises. With the increase of the temperature from 298 K to 333 K, their initial discharge capacity mounts up from 324.4 mA h g⁻¹ to 543.0 mA h g⁻¹ (when x = 0.2) and from 147.0 mA h g⁻¹ to 501.5 mA h g⁻¹ (when x = 0.4) at the current density of 31.25 mA g⁻¹, respectively. After 20 charge-discharge cycles, they still remain perovskite-type structure. Being similar to the relationship between the discharge capacity and the temperature, the electrochemical kinetic analysis indicates that the exchange current density and proton diffusion coefficient of La_(1−x)Sr_xFeO₃ oxide electrodes increase with the increase of the temperature. Compared with La_0.8Sr_0.2FeO₃, La_0.6Sr_0.4FeO₃ electrode is a more promising candidate for electrochemical hydrogen storage because of its higher cycle capacity at various temperatures.     

Electrochromic WO3−x films with reduced lattice deformation stress and fast response time

Electrochromic properties of electrochemically deposited and etched (EDE) WO_3−x films have been investigated using voltammetry and nanogravimetry to elucidate the amount of residual stress associated with lattice polarization and deformation in WO_3−x nanoparticles. The cathodic WO_3−x deposition from pertungstic acid solution and unusual properties of the cathodic electroetching of the oxide in tetraethyl ammonium chloride solution are reported and elucidated on the basis of Electrochemical Quartz Crystal Nanogravimetry (EQCN) measurements. The stress enhanced resonant frequency shift was observed upon WO_3−x film coloration. However, the stress enhancement appeared to be much lower (up to 4-6 times) than that measured for films synthesized by other methods. The stress reduction in WO_3−x films under study has been attributed to the stress relaxing propensity of EDE film to suppress the compressive stress wave. A considerable isotopic effect has been observed in nanogravimetry of the H⁺ and D⁺ ion intercalation into WO_3−x films. We have found that the isotopic effect is primarily due to the true mass loading difference between hydrogen and deuterium ions, for the same concentration of color centers (2.65 × 10²¹ cm⁻³), since EQCN frequency shifts associated with stress in the film for H⁺ and D⁺ are very close to each other.     

Structural and magnetic properties of Co1−xZnxFe2O4 nanorods prepared by the solvothermal annealing method

Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods have been prepared by the thermal decomposition of the corresponding oxalate precursor, which was synthesized by the template-, surfactant-free solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The obtained Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods were built by many nanoparticles with average sizes around 20 nm to form one-dimensional arrays. Vibrating sample magnetometry measurements show that the coercivity of the ferrite nanorods decreases with increasing Zn content, whereas the specific saturation magnetization initially increases and then decreases with the increase of Zn content. The maximum saturation magnetization value of the as-prepared sample (Co_0.5Zn_0.5Fe₂O₄) reaches 43.0 emu g⁻¹.     

Study on phase structure and electrochemical properties of Ml1−xMgxNi2.80Co0.50Mn0.10Al0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) hydrogen storage alloys

Phase structure and electrochemical properties of the Ml_1−xMg_xNi_2.80Co_0.50Mn_0.10Al_0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) (Ml = La-rich mixed lanthanide) alloys were studied. X-ray diffraction (XRD) analysis and Rietveld refinement show that the alloys consist mainly of LaNi₅ and (La,Mg)Ni₃ phase. Due to variation in phases of the alloys, the maximum discharge capacity, the high rate dischargeability (HRD), and the low temperature dischargeability increase first and then decrease. The maximum discharge capacity increases from 322 mAh g⁻¹ (x = 0.08) to 375 mAh g⁻¹ (x = 0.12), and then decreases to 351 mAh g⁻¹ (x = 0.28) with increasing x. As the case of x = 0.20, HRD at 1200 mA g⁻¹ and discharge capacity at 233 K reaches 41.7% and 256 mAh g⁻¹, respectively. The cycling stability is improved by substituting La with Ml and B-site multi-alloying, and the capacity retention of Ml_0.72Mg_0.28Ni_2.80Co_0.50Mn_0.10Al_0.10 at the 200th cycle is 71%.     

Double channel electrode flow cell application to the study of HO2 production on MnxCo3−xO4 (0 ≤ x ≤ 1) spinel films

We conducted a study on the electroreduction of O₂ in alkaline solution at room temperature on pure thin oxide electrodes of composition Mn_xCo_3−xO₄ (0 ≤ x ≤ 1) using the double channel electrode flow cell (DCEFC). The oxides were prepared at 150 °C and deposited by spray pyrolysis onto titanium substrates. The oxygen reduction reaction (orr) occurs through “interactive” and “parallel” pathways, and the ratio of O₂ molecules reduced to OH⁻ ions with respect to those reduced to HO₂⁻ ions depends on the oxide stoichiometry and on the applied overpotential. The formation of HO₂⁻ increases when the manganese concentration increases. The results obtained for the orr show that the number of electrons transferred per O₂ molecule decreases from 3 to 2 and the ratio k₁/k₂ (the rate constants for direct reduction to OH⁻ and indirect reduction to HO₂⁻) increases, respectively, in the overpotential studied range (−0.05 to −0.6 V). The Mn³⁺ ions placed in the B-sites of the spinel structure seem to be the active centres, where hydrogen peroxide is formed.     

Zr-doped Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) as cathode material for lithium ion batteries

Layered Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) have been prepared by the mixed hydroxide and molten-salt synthesis method. The individual particles of synthesized materials have a sub-microsize range of 200-500 nm, and LiNi_0.475Mn_0.475Zr_0.05O₂ has a rougher surface than that of LiNi_0.5Mn_0.5O₂. The Li/Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) electrodes were cycled between 4.5 and 2.0 V at a current density of 15 mA/g, the discharge capacity of both cells increased during the first ten cycles. The discharge capacity of the Li/LiNi_0.475Mn_0.475Zr_0.05O₂ cell increased from 150 to 220 mAh/g, which is 50 mAh/g larger than that of the Li/LiNi_0.5Mn_0.5O₂ cell. We found that the oxidation of oxygen and the Mn³⁺ ion concerned this phenomenon from the cyclic voltammetry (CV). Thermal stability of the charged Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) cathode was improved by Zr doping.     

Polypyrrole and La1−xSrxMnO3 (0≤ x ≤0.4) composite electrodes for electroreduction of oxygen in alkaline medium

Composite G/PPy/PPy(La_1−xSr_xMnO₃)/PPy electrodes made of the perovskite La_1−xSr_xMnO₃ embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La_1−xSr_xMnO₃) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm⁻³ pyrrole (Py) plus 0.05 mol dm⁻³ K₂SO₄ with and without containing a suspension of 8.33 g L⁻¹ oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm⁻³ K₂SO₄ plus 5 mmol dm⁻³ KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR.     

Structural and magnetic characterization of MnxZn1 − xFe2O4 (x = 0.2; 0.35; 0.65; 0.8; 1.0) ferrites obtained by the citrate precursor method

In this work the microstructure and magnetic properties of Mn-Zn ferrites powders were investigated. Mn_xZn1 _− xFe₂O₄ powders where x = 0.2; 0.35; 0.5; 0.65; 0.8 and 1.0 were obtained by citrate precursor method. Citrate resin precursor was burned on air atmosphere at 400 °C for 3 h. Mn-Zn powders were calcined at 950 °C during 150 min under inert atmospheres: N₂ and rarefied atmosphere. Thermal analysis of precursor resin, phase evolution and microstructure of Mn-Zn ferrites powders were investigated by TG, DTA, XRD and SEM techniques. The powders calcined under rarefied atmosphere show spinel cubic structure and contamination of α-Fe₂O₃, while powders calcined under N₂ presents only the spinel cubic structure. Particle size was observed by SEM ranging from 80 to 150 nm. The magnetic properties were measured employing a vibrating sample magnetometer (VSM). It was observed that the saturation magnetization M_s increased with the increase of Mn content. The M_s of Mn_0.8Zn_0.2Fe₂O₄ calcined on rarefied atmosphere and Mn_0.8Zn_0.2Fe₂O₄ calcined on N₂ was 23.31 emu g⁻¹ and 56.23 emu g⁻¹, respectively.     

Electrooxidation of formic acid on carbon supported PtxPd1−x (x = 0-1) nanocatalysts

In this work, carbon supported Pt_xPd_1−x (x = 0-1) nanocatalysts were investigated for formic acid oxidation. These catalysts were synthesized by a surfactant-stabilized method with 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as the stabilizer. They show better Pt/Pd dispersion and higher catalytic performance than the corresponding commercial catalysts. Furthermore, the electrocatalytic properties of Pt_xPd_1−x/C were found to depend strongly on the Pt/Pd deposition sequence and on the Pt/Pd atomic ratio. At a lower potential, formic acid oxidation current on co-deposited Pt_xPd_1−x/C catalysts increase with increasing Pd surface concentration. Nanoscale Pd/C is a promising formic acid oxidation catalyst candidate for the direct formic acid fuel cell.     

Preparation, characterization and electrical conductivity studies of NdYb1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics

Several compositions of NdYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 1.0) ceramics were prepared by pressureless-sintering method at 1973 K for 10 h in air. The relative density, microstructure and electrical conductivity of NdYb_1−xGd_xZr₂O₇ ceramics were analyzed by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance plots measurements. NdYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 0.3) ceramics have a single phase of defect fluorite-type structure, and NdYb_1−xGd_xZr₂O₇ (0.7 ≤ x ≤ 1.0) ceramics exhibit a single phase of pyrochlore-type structure; however, the NdYb_0.5Gd_0.5Zr₂O₇ composition shows mixed phases of both defect fluorite-type and pyrochlore-type structures. The measured values of the grain conductivity obey the Arrhenius relation. The grain conductivity of each composition in NdYb_1−xGd_xZr₂O₇ ceramics gradually increases with increasing temperature from 673 to 1173 K. NdYb_1−xGd_xZr₂O₇ ceramics are oxide-ion conductor in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 1.79 × 10⁻² S cm⁻¹ at 1173 K for NdYb_0.3Gd_0.7Zr₂O₇ composition.     

Effect of Mn content on the structure and electrochemical characteristics of La0.7Mg0.3Ni2.975−xCo0.525Mnx (x = 0-0.4) hydrogen storage alloys

The effect of Mn content on the crystal structure and electrochemical characteristics of La_0.7Mg_0.3Ni_2.975−xCo_0.525Mn_x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys has been studied systematically. The results of the Rietveld analyses show that all these alloys mainly consist of two phases: the La(La,Mg)₂Ni₉ phase with the rhombohedral PuNi₃-type structure and the LaNi₅ phase with the hexagonal CaCu₅-type structure. The pressure-composition isotherms shows that the partial substitution of Mn for Ni results in lower desorption plateau pressure and steeper pressure plateau of the alloy electrodes. For a Mn content of x = 0.3, the electrochemical performances, including specific discharge capacity, high rate chargeability (HRC) and high rate dischargeability (HRD), of the alloy are preferable. Moreover, the data of the polarization resistance R_p and the exchange current density I₀ of the alloy electrodes is consistent with the results of HRC and HRD. The hydrogen diffusion coefficient D increases with increasing Mn content, and thereafter increases the low temperature dischargeability (LTD) of the alloy electrodes.     

Synthesis and characterization of ZnxMg1 − xGa2O4:Co fabricated by low-temperature burning method

A series of Zn_xMg_1 − xGa₂O₄:Co²⁺ spinels (x = 0, 0.25, 0.5, 0.75, and 1.0) was successfully produced through low-temperature burning method by using Mg(NO₃)₂·4H₂O, Zn(NO₃)₂·6H₂O, Ga(NO₃)₃·6H₂O, CO(NH₂)₂, NH₄NO₃, and Co(NO₃)₂·6H₂O as raw materials. The product was characterized by X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The product was not merely a simple mixture of MgGa₂O₄ and ZnGa₂O₄; rather, it formed a solid solution. The lattice constant of Zn_xMg_1 − xGa₂O₄:Co²⁺ (0 ≤ x ≤ 1.0) crystals has a good linear relationship with the doping density, x. The synthesized products have high crystallinities with neat arrays. Based on an analysis of the form and position of the emission spectrum, the strong emission peak around the visible region (670 nm) can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴A₂(⁴F)] of Co²⁺ in the tetrahedron. The weak emission peak in the near-infrared region can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴T₂(⁴F)] of Co²⁺ in the tetrahedron.     

Ni1−xCox/YSZ cermet anodes for solid oxide fuel cells

Nanocrystalline and homogeneous powder mixtures of (Ni_1−xCo_xO_y)+YSZ were obtained by combustion synthesis, and reduced in H₂ at 800 °C to obtain Ni_1−xCo_x/YSZ cermets, and three layer symmetrical cells cermet/YSZ/cermet. These three layer cells were co-firing at 1450 °C, and then reduced to obtain porous Ni_1−xCo_x/YSZ cermet layers with good adhesion to the electrolyte. Results obtained under OCV show that partial substitution of Ni with Co lowers the polarisation resistance, especially the main contribution which is usually most dependent on the cermets microstructure. This trend is reverted for high fractions of Co, and the polarisation resistance obtained for Co/YSZ cermets is much higher than for Ni/YSZ. The low frequency contribution of the polarisation resistance was mainly dependent on the partial pressures of H₂ and H₂O, and is less dependent on the substitution of Ni with Co.     

One-step electrochemical preparation of the ternary (BixSb1−x)2Te3 thin films on Au(1 1 1): Composition-dependent growth and characterization studies

This study reports on the synthesis of ternary semiconductor (Bi_xSb_1−x)₂Te₃ thin films on Au(1 1 1) using a practical electrochemical method, based on the simultaneous underpotential deposition (UPD) of Bi, Sb and Te from the same solution containing Bi³⁺, SbO⁺, and HTeO₂⁺ at a constant potential. The thin films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-FTIR (RA-FTIR) to determine structural, morphological, compositional and optic properties. The ternary thin films of (Bi_xSb_1−x)₂Te₃ with various compositions (0.0 ≤ x ≤ 1.0) are highly crystalline and have a kinetically preferred orientation at (0 1 5) for hexagonal crystal structure. AFM images show uniform morphology with hexagonal-shaped crystals deposited over the entire gold substrate. The structure and composition analyses reveal that the thin films are pure phase with corresponding atomic ratios. The optical studies show that the band gap of (Bi_xSb_1−x)₂Te₃ thin films could be tuned from 0.17 eV to 0.29 eV as a function of composition.