Study of Pb-based and Pb-free perovskite solar cells using Cu-doped Ni1-xO thin films as hole transport material

SCAPS solar cell simulation program was applied to model an inverted structure of perovskite solar cells using Cu-doped Ni_1-xO thin films as hole transport layer. The Cu-doped Ni_1-xO film were made by co-sputtering deposition under different deposition conditions. By increasing the amount of the Cu-dopant, the film crystallinity enhanced whereas the bandgap energy decreased. The transmittance of the thin films decreased significantly by increasing the sputtering power of copper. High quality, uniform, compact, and pin-hole free films with low surface roughness were achieved. The structural, chemical, surface morphology, optical, electrical, and electronic properties of the Cu doped Ni_1-xO films were used as input parameters in the simulation of Pb-based (MAPbI_3-xCl_x) and Pb-free (MAGeI₃) perovskite solar cells. Simulation results showed that the performance of both Pb-based and Pb-free perovskite solar cell devices significantly enhanced with Cu-doped Ni_1-xO film. The highest power conversion efficiency (PCE) for the Pb-free perovskite solar cell is 8.9% which is lower than the highest PCE of 17.5% for the Pb-based perovskite solar cell.     

Effect of (Zn,Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe_1-2xZn_xMn_xO₃ (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO₃ (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10^?6 A/cm²) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm² was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm². The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.     

Effect of Mn-doping on the structure and electrical properties of (Pb0.325Sr0.675)TiO3 ceramics

Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti⁴⁺ and the valences of Mn ions were deduced to be mainly in the form of Mn²⁺ and/or Mn³⁺ for ceramics with low content of Mn, while the Ti ions were in the form of Ti³⁺ and Ti⁴⁺ and Mn ions were diverse valence states with the coexistence of Mn²⁺, Mn³⁺, and Mn⁴⁺ for ceramics with x?=?0.01 and 0.05.     

Subsolidus phase relationship in the Y2O3-Mn3O4-CoOx system in air

The subsolidus phase relations in the Y₂O₃-Mn₃O₄-CoO_x system in air were investigated by X-ray powder diffraction. All the samples were prepared by solid state reaction method. There are 8 single-phases, 9 two-phase regions and 8 three-phase regions in this system. Two solid solutions, namely o-YCo_xMn_1-xO_3-δ with a narrow range of 0.70 ≤ x ≤ 0.76 and m-YCo_xMn_1-xO_3-δ with a wider range of 0.28 ≤ x ≤ 0.60, were found to form. o-YCo_xMn_1-xO_3-δ crystallizes in an orthorhombic Pnma perovskite structure, while m-YCo_xMn_1-xO_3-δ exhibits diffraction features of either monoclinic P2₁/n or/and orthorhombic Pnma perovskite structure. The homogeneity ranges for hexagonal YMnO₃ (less than 3 at. % CoO), orthorhombic YMn₂O₅ (less than 4 at. % CoO) and the tetragonal spinel phase t-Co_xMn_3-xO₄ (0-31 at. % CoO), the cubic spinel phase c-Co_xMn_3-xO₄ (65-69 at. % CoO) were determined.     

Multifunctional properties of Zn0·9Mn0.05M0.05O (M = Al,Bi, Sr,Ag) nanocrystals-structural and optical study: Enhance sunlight driven photocatalytic activity

Novel Zn_0·95Mn_0·05O and Zn_0·9Mn_0.05M_0.05O (M = Al, Bi, Sr, Ag) nanocrystals were prepared via the co-precipitation technique. The X-ray diffraction pattern confirmed the substitution of Mn, Al, Bi, Sr, and Ag dopants without altering the basic ZnO structure. The microstructural study was performed by employing the Scherrer plot, Williamson-Hall, and SSP methods. The energy bandgap calculated from UV–vis spectra using different methods observed red-shifted by co-doping. The other optical parameters were also studied and discussed in detail. The FTIR spectra confirmed the presence of Zn–O, and Zn-M–O vibrational modes. Raman spectra demonstrated the presence of ZnO phonon modes, and the Raman shift exhibited the structural defects induced by dopants. The PL spectra showed strong NBE and DLE in the UV and visible region due to extrinsic defects. The IV measurements exhibited the enhancement in the electrical conductivity of ZnO by co-doping. The photocatalytic activity was performed under direct sunlight for methyl orange and methylene blue dyes, and the enhanced degradation efficiency was achieved by co-doping. Furthermore, this article enhances the understanding of tuning the physical properties of ZnO by co-doping and introduces a new class of sunlight-driven photocatalysts.     

Moisture sensitivity of YCr(1−x)MnxO3 perovskites

This work deals with the sensitivity to moisture rate in air of perovskite with general formula YCr_(1−x)Mn_xO₃ with x ranging from 0 to 0.8. The combined sensitivity to moisture and temperature let us think the possibility of realizing composite sensors temperature/moisture. This study clearly shows the influence of the Mn content on moisture which affects the working frequency of sensors. Capacitance variation of the most sensitive compositions increases from 100 pF to 1 nF for relative humidity between 20 and 80%. The influence of porosity is also demonstrated.     

Effects of ionic radius on phase evolution in Ln-Al co-doped Ca1-xLnxZrTi2-xAlxO7 (Ln = La,Nd, Gd,Ho, Yb) solid solutions

Zirconolite ceramic has been considered as a promising matrix to dispose high-level radioactive waste due to its excellent performance in immobilizing radionuclides. In this work, a series of zirconate solid solutions with stoichiometric Ca_1-xLn_xZrTi_2-xAl_xO₇ (Ln = La, Nd, Gd, Ho, Yb; x?=?0.1–1) were systematically studied to investigate the radius effect on their phase evolution. Powder X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-Ray spectrometry (SEM-EDX) were used to characterize the products. XRD and SEM results show that complete solid solutions of Ln and Al in zirconolite phase for Ca_1-xLn_xZrTi_2-xAl_xO₇ cannot found. In the Ca_1-xLa_xZrTi_2-xAl_xO₇ ceramics, single zirconolite phase cannot form, instead of multiple phases, such as zirconolite-2M, zirconia, perovskite and LaTi₂Al₉O₁₉. In the Nd-Al co-doping ceramics, nearly single zirconolite-2M and zirconolite-3O were found at x?≤?0.6 and 0.8?≤?x?≤?0.9, respectively. The miscibility gap between zirconolite-2M and 3O was found at x?=?0.7. Single zirconolite-2M formed in the Gd-Al, Ho-Al and Yb-Al co-doped ceramics can only be detected in a compositional range of 0.1?≤?x?≤?0.8. Higher incorporation contents in these three series can form an additional phase cubic zirconia which is usually a ceramic waste form for radionuclides. Based on the XRD data, lattice parameters of zirconolite-2M and zirconolite-3O were calculated by Pawley refinement method. The evolution of lattice parameters of zirconolite-2M shows great difference between different lanthanide ions, indicating different substitution mechanisms in the Ln-Al co-doped zirconolite-2M.     

Halogen-content-dependent photoluminescence of Mn2+-doped CsPbCl3 nanocrystals

The thermodynamically viable halogen vacancy defects in CsPbCl₃ perovskite nanocrystals (NCs) are considered the main factor in weakening their optical quality. However, their separate impact on the dopant emission in Mn²⁺-doped CsPbCl₃ perovskite NCs is still under exploration owing to the absence of comparable samples. Herein, a series of Mn²⁺-doped CsPbCl₃ samples were synthesized with different oleylamine-Cl (OAm-Cl) contents based on a halogen-hot-injection strategy. It is found that the Mn²⁺ concentration of as-prepared samples fixed at 0.65%, and the Mn²⁺ photoluminescence (PL) also exhibited an OAm-Cl content-independent lifetime of ∼ 1.78 ms, implying the efficient and identical luminescence of isolated Mn²⁺ ion in all samples. In contrast, the excitonic and Mn²⁺ PL intensities of the NCs are strong related to the amount of OAm-Cl, which are attributed to the coordination effect of the suppressed excitonic nonradiative recombination owing to the passivation of chloride vacancies and the enhanced energy transfer from the host exciton to Mn²⁺ ions in the samples with sufficient OAm-Cl contents. The temperature-dependent of Mn²⁺ PL disclosed an initial increase and was followed by a decrease with increasing temperature for the samples with relatively higher OAm-Cl contents, while it monotonously decreases for the sample with lower OAm-Cl content of 0.4 mL. The different PL intensity change trend results from the effective passivation of chloride vacancies by extra OAm-Cl. Above results present here will help clarify the underlying influence mechanism of halogen vacancy on the PL properties of Mn²⁺-doped perovskite NCs, which is essential for targeted modulation of their optical properties.     

Mn1-xCuxO2/ reduced graphene oxide nanocomposites: Synthesis,characterization, and evaluation of visible light mediated catalytic studies

The narrow optical band gap, higher electrical conductivity, and wider-absorption range are three key features that a good photocatalyst must possess. Herein, we have fabricated Cu-doped MnO₂ (Mn_1-xCu_xO₂) nanostructure by facile wet chemical approach and formed its nanocomposite with r-GO (Mn_1-xCu_xO₂/r-GO) via ultra-sonication approach. The successful replacement of host metal ions (Mn⁴⁺) with the dopant metal ions (Cu²⁺) was supported with the PXRD, FT-IR, and EDX characterizations. The effect of Cu-doping on the band gap and r-GO matrix on the conductivity of the fabricated nanocomposite was also evaluated via Tauc plots and I–V tests, respectively. The photocatalytic efficiency of the fabricated photocatalysts was tested and compared against the methylene blue (MB) under visible light irradiation. The photocatalytic experiments revealed that Mn_1-xCu_xO₂/r-GO photocatalyst exhibited superior photocatalytic aptitude than that of pristine MnO₂ and Mn_1-xCu_xO₂ photocatalysts. More precisely, the Mn_1-xCu_xO₂ photocatalysts degraded 86.89% MB dye at the rate of 0.021 min^?1 after a 90-min exposure to the visible light. Observed superior catalytic activity of the nanocomposite can be attributed to the synergistic effects between the Cu doped MnO₂ and r-GO nanosheets that resulted in its narrow band-gap (2.19 eV) and excellent conductivity (2.217 × 10^?2 Scm^?1).     

Enhanced visible light photocatalytic performance of Sr0.3(Ba,Mn)0.7ZrO3 perovskites anchored on graphene oxide

In search of better materials for visible light photocatalytic performance, perovskite Sr_0.3(Ba/Mn)_0.7ZrO₃ nanopowders anchored on graphene oxide were synthesized for the evaluation of their photocatalytic activity against methylene blue (MB). The chemical coprecipitation method was used to synthesize SrZrO₃ (SZO) and a series of doped derivatives having a nominal composition of Sr_1-x(Ba,Mn)_xZrO₃ (x = 0.1–0.9) at an annealing temperature of 700 °C for 12 h. However, Sr_0.3(Ba,Mn)_0.7ZrO₃ with a bandgap value of 3.50 eV was further processed for the formation of composite with graphene oxide (GO) owing to its lowest bandgap value in the synthesized series. The inclusion of larger Ba²⁺ cations in the lattice resulted in the redistribution of cations creating antisite defects which were evident from the shrinkage of the lattice. The incorporation of Mn²⁺ resulted in the hybridization of Mn²⁺ (3d) orbitals with the split Zr⁴⁺ (4d) orbitals. This reduced the bandgap and composite formation with GO further enhancing the delocalization of excited electrons to GO hence, reducing electron-hole recombination. Adsorption assisted photocatalysis under a 100 W tungsten lamp was performed using the designed catalysts for the removal/degradation of MB. The π-π conjugation and the ionic interactions were found responsible for the adsorption of MB at the GO surface. High surface coverage, initial dye concentrations, heterogeneous catalyst surface, weak van der Waals interactions, pH and availability of ?OH radicals were found to be the decisive factors for the removal/degradation process. Improved charge separation enhances the generation of ?OH and better performance of the GO composites as opposed to the pristine strontium zirconate perovskites.     

Photo-synaptic properties of CH3NH3Pb1-xMnxBr2x+1 hybrid perovskite thin film-based artificial synapse

With the increasing demands on unstructured data processing, a system emulating the human nervous system has garnered great attention as an alternative to the von-Neumann architecture due to low power consumption and parallel data processing. To realize the neuromorphic computing, the artificial electronic synapse, neuron device and architecture have been investigated using various materials and devices. In this regard, in addition to electrical-responsive synaptic devices, photoresponsive synapse devices are attracting attention due to photoresponse with high bandwidth, low power consumption, and low current crosstalk. Espicially, the organic-inorganic hybrid halide perovskites (OIHPs) are promising materials for photodevices due to broad optical absorption, low exciton binding energy, fast charge transport properties, and tunable bandgap. The OIHPs have been implemented to demonstrate the photo-stimulated synaptic functions, however, most OIHPs contain toxic lead cations, limiting their widespread application. In this study, we investigated the light-stimulated photosynaptic characteristics based on OIHPs synthesized with Mn²⁺ (CH₃NH₃Pb_1-xMn_xBr_2x+1) that could substitute non-desirable Pb-based perovskite. The Mn²⁺-based OIHPs photosynapstor successfully emulated the essential synaptic characteristics including excitatory post-synaptic current, pulse-paired facilitation, post-tetanic potentiation, transition from short-term plasticity to long-term plasticity, forgetting curve, and spike-timing dependent plasticity.     

Influence of manganese substitution into the A-site of perovskite type Ca1−xMnxTiO3 ceramic

Ca_1−xMn_xTiO₃ (x = 0–1.0) perovskite ceramics were prepared by conventional solid state reaction. XRD was used to confirm the microcrystalline nature of the Ca_1−xMn_xTiO₃ crystals. For the x = 0 composition, the XRD patterns were those of a single orthorhombic perovskite while for x = 0.2–0.8, the XRD spectra were those of two orthorhombic perovskite phases: CaTiO₃ and MnTiO₃. For x = 1, XRD pattern was that of the MnTiO₃ phase only. The morphology and particle size of the grains of the different composition were observed using SEM. The size of the particles increased from 0.2 μm to 2–3 μm as x increased from 0 to 0.6. The room temperature dielectric constant at the frequency of 110 kHz for the x = 0.2 and x = 1.0 ceramics were ∼3.41 × 10⁴ and ∼4.99 × 10³, respectively. The ESR linewidth of samples increased with increasing manganese content due to the formation of magnetic cluster. Our ESR studies indicate that the manganese ions are in the Mn⁴⁺ state.     

Tuning the luminescence properties of Mn4+-activated CaYAlO4 phosphor by co-doping cations for indoor plant cultivation

To fulfil the demands of high-power plant growth lamps, cation co-doping is an effective way to tune the photoluminescence properties of manganese (Ⅳ)-activated aluminate phosphors. Therefore, we managed to synthesize a series of cations co-doped CaYAlO₄:xMn⁴⁺, mSr²⁺, M⁺ (M⁺ = Li⁺, Na⁺, and K⁺) (CYAO:Mn, Sr, M) far-red-emitting phosphors. The excitation spectrum of these phosphors contained two excitation bands, and the opposite effects of these two bands on the luminescence intensity have been observed with the increase of Mn⁴⁺ concentration. By adding 0.1 mol Sr²⁺ ions to replace Ca²⁺ site, the emission intensity and thermal stability of CYAO:Mn phosphors can be enhanced. Furthermore, the luminescence properties of CSYAO:Mn can be further improved by co-doping monovalent alkali metal ions to serve as charge compensators, the increased number of Mn⁴⁺ luminescence centers. Moreover, 0.6 mol% Na⁺ can increase the initial emission intensity of the phosphors by 117% as the best ratio. The characteristic emission spectrum of the phosphors CYAO:Mn,Sr,M correspond to the phytochrome P_FR of plants. These experiments and characterization results have certified that these phosphors have a potential application in indoor plants cultivation.     

Temperature dependent negative permittivity in solid solutions Sr2Mn1-xSnxO4 (x = 0, 0.3, 0.5)

A few compositions of the system Sr₂Mn_1-xSn_xO₄ (x = 0.0, 0.3, 0.5) were synthesized in the air by the solid-state ceramic route. A change in the sign (positive to negative) of the permittivity above a particular temperature (T_C) is observed at all the measured frequencies. The negative permittivity was analyzed by the Drude-Lorentz model. It was found that negative permittivity is caused by the plasma oscillations of thermally excited free charge carriers. Analysis of XPS spectra confirmed the presence of mixed-valence states of both Mn (Mn⁴⁺ and Mn³⁺) and Sn (Sn⁴⁺ and Sn²⁺) ions. The UV–vis.-IR spectroscopy results indicated generation of a large number of defect states in the forbidden bandgap region of Sr₂MnO₄ on the substitution of Sn at Mn site. Synthesized samples are promising metamaterials for radio frequency (10 Hz -2 MHz) region applications due to the high-temperature plasmonic behavior.     

High dielectric and microwave absorption properties of ultra-thin 1-xSrTiO3-δ − xSrAl12O19 films

To reduce the thickness of the microwave absorbing materials, we have prepared 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ ceramics by hot?pressing sintering in the vacuum. The microstructure, dielectric, thermogravimetric analysis and microwave absorbing properties of 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ were systematically investigated and discussed. The 0.95SrTiO_3-δ??0.05SrAl₁₂O₁₉ has high permittivity, the real part is from 1662.2 to 704.9 and the imaginary part is from 208.6 to 12. The absorption bandwidth (reflection loss ≤?5?dB) of 0.95SrTiO_3-δ??0.05SrAl₁₂O₁₉ can cover 8.6???12.4?GHz and its thickness is only 0.232?mm which is much thinner than these recently reported by other researchers. For 0.942SrTiO_3-δ??0.058SrAl₁₂O₁₉, the peak value of reflection loss is up to ??58.5?dB with a thickness of 0.75?mm. The 1-xSrTiO_3-δ?xSrAl₁₂O₁₉ films could be excellent candidates for highly efficient and ultra?thin microwave absorbing materials.     

Tuning magnetic properties of BiFeO3 thin films by controlling Mn doping concentration

Mn-doped BiFeO₃ (BiFe_1–xMn_xO₃, x = 0, 0.03, 0.05, 0.10, 0.15 and 0.20) polycrystalline multiferroic thin films were successfully synthesized using the facile sol-gel spin-coating method. The crystal structures, surface features, elements valences, and magnetic properties of as-prepared samples were systematically explored. X-ray diffraction and Raman spectroscopy studies revealed the substitutions of Mn into the Fe site and a rhombohedral-to-orthorhombic phase transition. The Field Emission Scanning Electron Microscopy showed a decrease in the average particle sizes and an improvement of surface morphology with increasing the concentration of the substitutes. Energy-dispersive X-ray spectroscopy confirmed the doping concentration of Mn²⁺ in the samples. X-ray photoelectron spectroscopy indicated the co-existence of Mn²⁺/Mn³⁺ ions in the doped films. The remnant magnetization value of BiFe_0.90Mn_0.10O₃ thin film was found to be approximately six times than that of pure BiFeO₃ thin film under a magnetic field of 10 kOe. The enhanced magnetic property of BiFe_0.90Mn_0.10O₃ thin film was mainly ascribed to the structural distortion of spin cycloid and the enhancement of super-exchange interaction between the Fe³⁺ (Mn²⁺) and O^2- ions.     

Effects of Al substitution for Ni and Mn on the electrochemical properties of LiNi0.5Mn1.5O4

The effects of Al substitution for Ni or (and) Mn in LiNi_0.5Mn_1.5O₄ spinel on the structures and electrochemical properties are investigated. Powders of LiNi_0.5Mn_1.5O₄, Li_0.95Ni_0.45Mn_1.5Al_0.05O₄, LiNi_0.475Mn_1.475Al_0.05O₄ and Li_1.05Ni_0.5Mn_1.45Al_0.05O₄ are synthesized by a thermopolymerization method. Their structures and electrochemical properties are studied by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, cyclic voltammetry and galvanostatic charge–discharge testing. The introduction of Al in these LiNi_0.5Mn_1.5O₄ samples has resulted in structure variation, and greatly improved their cyclic performance and rate capability. The effects of Al substitutions for Ni and Mn in the LiNi_0.5Mn_1.5O₄ are different. Compared with LiNi_0.5Mn_1.5O₄, Li_0.95Ni_0.45Mn_1.5Al_0.05O₄ demonstrates higher specific capacity at room temperature but faster capacity fading at elevated temperatures. Li_1.05Ni_0.5Mn_1.45Al_0.05O₄ displays a lower discharge capacity but better capacity retention at 55 °C. Moreover, the cyclic performance and rate capability of the Ni-substituted Li_0.95Ni_0.45Mn_1.5Al_0.05O₄, Ni/Mn co-substituted LiNi_0.475Mn_1.475Al_0.05O₄ and Mn-substituted Li_1.05Ni_0.5Mn_1.45Al_0.05O₄ at room temperature are similar, and have improved substantially compared with the Al-free LiNi_0.5Mn_1.5O₄ sample.     

Tunable luminescence properties and efficient energy transfer in Eu,Mn co-doped Ba2MgP4O13

A series of Ba₂Mg_1−xMn_xP₄O₁₃ (x = 0-1.0) and Ba_1.94Eu_0.06Mg_1−xMn_xP₄O₁₃ (x = 0-0.15) phosphors were prepared by conventional solid-state reaction. X-ray powder diffraction (XRD), the photoluminescence spectra, and the decay curves are investigated. XRD analysis shows that the maximum tolerable substitution of Mn²⁺ for Mg is about 50 mol% in Ba₂MgP₄O₁₃. Mn²⁺-singly doped Ba₂MgP₄O₁₃ shows weak red-luminescence peaked at about 615 nm. The Eu²⁺/Mn²⁺ co-doped phosphor emits two distinctive luminescence bands: a blue one centered at 430 nm originating from Eu²⁺ and a broad red-emitting one peaked at 615 nm from Mn²⁺ ions. The luminescence of Mn²⁺ ions can be greatly enhanced with the co-doping of Eu²⁺ in Ba₂MgP₄O₁₃. The efficient energy transfer from Eu²⁺ to Mn²⁺ is verified by the excitation and emission spectra together with the luminescence decay curves. The emission colors could be tuned from the blue to the red-purple and eventually to the deep red. The resonance-type energy transfer via a dipole-quadrupole interaction mechanism is supported by the decay lifetime data. The energy transfer efficiency and the critical distance are calculated and discussed. The temperature dependent luminescence spectra of the Eu²⁺/Mn²⁺ co-doped phosphor show a good thermal stability on quenching effect.     

Structural,morphological, and electrochemical behavior of titanium-doped SrFe1-xTixO3-δ (x = 0.1–0.5) perovskite as a cobalt-free solid oxide fuel cell cathode

Titanium, Ti-doped SrFe_1-xTi_xO_3-δ (x = 0.1–0.5) perovskite-structured ceramics were synthesized via solution combustion. The structural, morphological, and electrochemical behaviors of the as-synthesized materials were investigated to determine the applicability of SrFe_1-xTi_xO_3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells. X-ray diffraction analysis confirmed the formation of a single-phase cubic perovskite structure. The unit volume of this perovskite structure increased as the amount of Ti dopant increased. Morphological analysis revealed that the porosity of the SrFe_1-xTi_xO_3-δ perovskite cathode film was inversely proportional to the amount of Ti dopant. The cathode SrFe_0·9Ti_0·1O_3-δ film exhibited a high porosity of 24.74 ± 0.52%, a low but acceptable hardness value of 0.70 ± 0.01 GPa and an area specific resistance of 0.57 Ω cm². These results suggested that cobalt-free SrFe_1-xTi_xO_3-δ cathode was still not good enough to be compared with the existing cobalt-containing cathode such as lanthanum strontium cobalt ferrite. But, the results obtained from this work can be considered as a major turning point as the literature works on SrFe_1-xTi_xO_3-δ cathode showed excellence electrochemical performance. The contradict result between the present and past studies proved that the use of SrFe_1-xTi_xO_3-δ cathode is worthy of being studied into details to confirm its capability.     

Enhanced sinterability and conductivity of cobalt doped lanthanum niobate as electrolyte for proton-conducting solid oxide fuel cell

La_0.95Ca_0.05Nb_1-xCo_xO₄ (x?=?0, 0.01, 0.02, 0.03, 0.05) compounds have been synthesized by a conventional solid state reaction method at 1150?°C. Co and Ca have been simultaneously introduced into LaNbO₄ solid solution for the first time, taking the place of La and Nb sites, respectively. Dense ceramic pellets of La_0.95Ca_0.05Nb_1-xCo_xO₄ have been prepared by sintering at 1300?°C with the utilization of cobalt as the sintering aid. The conductivity measurement has been carried out for all the samples in wet air. The results demonstrate that conductivity of La_0.95Ca_0.05Nb_1-xCo_xO₄ compounds are higher than that of LaNbO₄ attributed to additional oxygen vacancies generated by Co and Ca co-doping. The strategy of doping cobalt as a sintering aid proposed in this work could be served as a valid way to enhance the sinterability and electrical conductivity of LaNbO₄ based proton conducting oxides.