A-site Ca/Sr co-doping to optimize room-temperature TCR of La0.7Ca0.3-xSrxMnO3 films

Based on the analysis of crystal structure, Mn³⁺/Mn⁴⁺ pairs, distortion of MnO₆ octahedron, and electrical transport properties of La_1-xCa_xMnO₃ and La_1-xSr_xMnO₃ materials, room-temperature coefficient of resistivity (TCR) of La_0.7Ca_0.3-xSr_xMnO₃ (LCSMO) films was optimized by Ca/Sr co-doping at the A-site. LCSMO films are successfully fabricated on LaAlO₃ (100) substrates via facile spin coating technology. The microstructure of LCSMO films is characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy and X-ray photoemission spectroscopy. Results reveal that A-site Ca/Sr co-doping significantly influenced crystal structure, formation of Mn³⁺/Mn⁴⁺ pairs, and distortion of MnO₆ octahedron. The correlation between microstructure and electrical transport properties was explained through the phenomenological percolation model, double-exchange mechanism and Jahn-Teller effect. Furthermore, the TCR reached 10.2% K^-1 at 296.1 K in La_0.7Ca_0.18Sr_0.12MnO₃ films.     

Synthesis of La1−xSrxMnO3 powders by polymerizable complex method: Evaluation of structural, morphological and electrical properties

Lanthanum strontium manganite (La_1−xSr_xMnO₃, LSM) powders were synthesized by polymerizable complex method, based on complexation of metal ions (MI) with citric acid (CA) and polyesterification between CA and ethylene glycol (EG). Firstly, the effect of the molar ratio of CA:MI (=1–3) was investigated on the synthesis of La_0.7Sr_0.3MnO₃ powders, which were characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the molar ratio CA:MI = 3 is adequate for a good crystallization of pure perovskite phase after calcination, with nanometric crystallite sizes and porous microstructure. For the La_0.7Sr_0.3MnO₃ sample synthesized with CA:MI ratio of 3, it was investigated the effect of calcination temperature, showing that the perovskite structure is better crystallized at 900 °C, without secondary phase formation. Using this same CA:MI ratio and calcination temperature, powders with different Sr content (x = 0.2–0.4) were synthesized, with surface areas of 4–10 m² g⁻¹. These powders were sintered at 1100 °C to produce porous pellets. The porosity of the sintered pellets and the electrical conductivity, measured by two-probe technique, increased with increasing Sr content.     

Effect of Fe substitution on temperature coefficient of resistance and magnetoresistance of La0.67Ca0.33MnO3 polycrystalline ceramics

La_0.67Ca_0.33MnO₃ perovskite manganate exhibits high temperature coefficient of resistance (TCR) and large magnetoresistance (MR) effect, these enable novel multifunctionalities. Mn site substitution can change magnetic order of the manganates, thereby tailoring both electrical and magnetic transport. Herein, La_0.67Ca_0.33Mn_1-xFe_xO₃(0 ≤ x ≤ 0.06) polycrystalline ceramics were prepared by sol-gel route. The effect of Fe substitution on TCR and MR of La_0.67Ca_0.33MnO₃ was studied. Fe replacing Mn ions, would weaken double exchange, and significantly reduced Curie temperature and ferromagnetism. Additionally, Fe doping promoted the development of grain. TCR increased first with Fe content x and then decreased, and reached 45.2%·K^-1 at x = 0.01, which is the highest value reported. Notably, with Fe doping, MR gradually increased and reached 81.1% (1 T) at x = 0.06. Fe doping can significantly enhance TCR and MR, which generates promising potential in (uncooled) thermistor/infrared detecting and magnetic sensors.     

(La,Sr)(Mn,Me)O3 manganites doped with d metals: Study of charge compensation mechanisms by crystallographic and magnetic characterizations

A comparison between theoretically calculated unit cell volume and interatomic distances in the system La_0.7Sr_0.3Mn_1−xMe_xO_3+δ (where Me = Cu, Fe, Cr, Ti) and the experimental data obtained by the full-profile Rietveld X-ray analysis as well as an analysis of magnetic properties allowed us to suggest possible mechanisms of charge compensation occurring when d metals substitute for manganese. It has been shown that in the case when copper, iron, chromium and titanium ions substitute for manganese ions in the system La_0.7Sr_0.3Mn_1−xMe_xO₃ charge compensation is described by the model 2Mn³⁺ → Mn⁴⁺ + Cu²⁺, Mn³⁺ → Fe³⁺, Mn³⁺ → Cr³⁺ and Mn⁴⁺ → Ti⁴⁺, respectively. In the latter case, a decrease in oxygen nonstoichiometry occurs with increasing x.     

Electrochemical properties of Sr1−xCexMnO3 (0.1≤x≤0.4) – GDC composite cathodes for IT-SOFCs

The electrochemical properties of Sr_1−xCe_xMnO₃ (SCM, 0.1≤x≤0.4)–Gd_0.2Ce_0.8O_2−x (GDC) composite cathodes were determined by impedance spectroscopy. The study focused on the doping effect of Ce in the composite cathodes. Single-phase perovskite was obtained for 0.1≤x≤0.3 in SCM. No reaction occurred between the Sr_0.7Ce_0.3MnO₃ electrode and the GDC electrolyte at an operating temperature of 800 °C for 100 h. In the single phase perovskite region, lattice expansion occurred due to the reduction of Mn⁴⁺ to Mn³⁺ at B-sites, and this was attributed to an increase in Ce content. Ce doping enhanced the electrode performance of SCM–GDC composite cathodes, and best electrode performance was achieved for the Sr_0.7Ce_0.3MnO₃–GDC composite cathode (0.93 Ω cm² and 0.47 Ω cm² at 750 °C and 800 °C, respectively). The improvement in electrode performance was attributed to increases in charge carriers induced by a shift of some Mn from +4 to +3 and to the formation of surface oxygen vacancies caused by Mn⁴⁺ to Mn³⁺ conversion at high temperatures.     

Effects of Particle Size on Electromagnetic and Microwave Absorption Properties of La0.7Sr0.3MnO3±δ‐Epoxy Composite

La_0.7Sr_0.3MnO_3±δ powders were fabricated by solid‐state reaction method at 1473 K for 4 h. The precursors were prepared by ball‐milling raw materials for 3, 6, 9, and 12 h, respectively. The crystal structures, particle size, and morphologies of precursors and prepared La_0.7Sr_0.3MnO_3±δ were characterized by XRD, laser particle size analyzer and SEM, respectively. It is found that La_0.7Sr_0.3MnO_3±δ possessed large particle size by ball‐milling raw materials for a long time. Results indicated that La_0.7Sr_0.3MnO_3±δ, synthesized by ball‐milling raw materials for 3 h, exhibited the optimal microwave absorption properties. The maximum reflection loss was ?28.8 dB, and the ?6 dB absorption bandwidth was 5.80 GHz.     

Synthesis and electrochemical characterization of La0.75Sr0.25Mn0.5Cr0.5−xAlxO3, for IT- and HT-SOFCs

The main emphasis of this work is to create a new perovskite material with three different compositions (La_0.75Sr_0.25Mn_0.5Cr_0.5−xAlxO₃, x = 0.1, 0.2, 0.3) applied in both Intermediate- and High-temperature Solid Oxide Fuel Cells (IT- and HT-SOFCs). Perovskite-type polycrystalline La_0.75Sr_0.25Mn_0.5Cr_0.5−xAl_xO_3−δ (x = 0.1, 0.2, 0.3) powders were synthesized and formed in a single phase structure by a dry chemistry route (standard solid-state reaction method). The effect of Al doping on physicochemical and surface properties has been discovered. The compounds were crystallized in single phase rhombohedral symmetry (R-3C Space. Group). Total conductivity of Al doping in wet 5% H₂ was higher than both dry 5% H₂ and air. The obtained results enhance the electro-catalytic performance and the material conductivity as well, which will be good for anode materials in IT- and HT-SOFCs and the optimum doping is 10%.     

Structural,magnetic and magnetocaloric study of La0.7−xEuxSr0.3MnO3 (x=0.1, 0.2 and 0.3) manganites

This paper reports the structural, magnetic and magnetocaloric properties of La_0.7−xEu_xSr_0.3MnO₃ (x=0.1, 0.2 and 0.3) polycrystalline manganites elaborated using the solid-state reaction at high temperatures. The X-ray powder diffraction shows that all the prepared compounds are single phase. La_0.6Eu_0.1Sr_0.3MnO₃ is crystallized in the rhombohedral symmetry, whereas a structural transition towards orthorhombic system is observed for x≥0.2. Eu doping was found to induce a decrease of the Curie temperature T_C from 343 K (x=0.1) to 272 K (x=0.3). All compounds undergo a large magnetocaloric effect and have consequently potential applications in magnetic refrigeration domain around room temperature.     

Enhanced temperature coefficient of resistance and magnetoresistance of Co-doped La0.67Ca0.33MnO3 polycrystalline ceramics

Recently, La_0.67Ca_0.33MnO₃ has garnered significant research attention due to its peculiar physical properties, such as colossal magnetoresistance and metal insulator transitions. The practical applications of these materials are mainly determined by the temperature coefficient of resistance (TCR) and magnetoresistance (MR). As a mature synthesis route, the sol-gel method can prepare high-quality ceramic targets. Herein, using methanol as a solvent, La_0.67Ca_0.33Mn_1-xCo_xO₃ (0 ≤ x ≤ 0.06) polycrystalline ceramics are prepared using the sol-gel method and the influence of Co doping on electrical and magnetic properties is systematically studied. Co doping increases the grain size, and is helpful to improve TCR and MR. In addition, with increased Co doping, the double exchange is weakened, and the ferromagnetism is depressed, which leads to a decrease in T_MI. The results reveal that the TCR and MR can be optimized by tuning the Co content. For instance, we have achieved a TCR value of 44.2% · K^?1 at x = 0.02 and an MR value of 76.3% at x = 0.04, showing the promise of Co-doped La_0.67Ca_0.33MnO₃ ceramics in a wide array of applications, such as bolometers and magnetic sensors.     

Structural analysis and electrode performance of Ce doped SrMnO3 synthesised by EDTA citrate complexing process

Abstract

Sr_1?xCe_xMnO₃ (SCM, 0·1≤x≤0·4) powders were synthesised by an ethylenediaminetetraacetic acid citrate complexing process, and their properties were investigated. The synthesised Sr_1?xCe_xMnO₃ powders showed a pure perovskite phase, whereas the composition with x?=?0·4 had second phases. The unit cell volumes increased with increasing Ce content because substituted Ce ions formed some Mn³⁺ ions, which have a larger ionic radius than Mn⁴⁺. The electrical conductivity improved with increasing Ce content up to x?=?0·3 (291 S cm^?1 at 750°C), revealing a double exchange interaction. Although the electrical conductivity was increased by doping Ce ions, the polarisation resistance increased due to the increase in lattice distortion with doping Ce content. The substitution of Ce ions for Sr in SrMnO₃ led to the formation of larger Mn³⁺ ions than Mn⁴⁺ ions and lattice distortion, which would affect the electrical and oxygen ion conductivity.     

Effects of Sr doping on the structure,magnetic properties and microwave absorption properties of LaFeO3 nanoparticles

Lightweight, broadband microwave absorbing materials, with strong absorption capacities, are an urgent demand for practical applications. The microstructural and microwave absorption properties of LaFeO₃ samples prepared by a sol-gel method using different amounts of Sr are investigated systematically. X-ray diffraction and Rietveld refinement studies showed that Sr²⁺ doping can distort the crystal structure of LaFeO₃, leading to lattice expansion and spin tilt of the Fe-O-Fe bond angle. The improvement of magnetic properties mainly originates from the synergistic effect of the bond angle spin tilt and crystal structure defects. Oxygen vacancies will be generated due to the fluctuations in the valence state of Fe³⁺ resulting from the substitution of La³⁺ by Sr²⁺ as deduced from the X-ray photoelectron spectroscopy analysis. The generation of oxygen vacancies, electronic hopping and polarization loss may be one of the main reasons for changes in the electromagnetic parameters. The minimum reflection loss (RL) of La_1–xSr_xFeO₃ nanoparticles with the Sr doping of 0.2 can reach approximately -39.3 dB at 10 GHz for the thickness of 2.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) can reach approximately 2.56 GHz. In addition, the La_1–xSr_xFeO₃ nanoparticles also can obtain better microwave absorbing performance in the C-band (4–8 GHz) with the minimum RL of -36.8 dB for the matching thickness of 3.0 mm and Sr content of 0.3. Consequently, La_1–xSr_xFeO₃ nanoparticles are promising materials for use in a high-performance and adjustable electromagnetic wave absorber, particularly in C-band and X-band.     

Rapid and high sensing response to acetone based on La1-xBaxMnO3+δ nanopowders

Different La_1-xBa_xMnO_3+δ nanopowders (with x = 0–0.20) were prepared using a traditional sol-gel method. Each sample had a size distribution between 50 and 80 nm with a single perovskite-type structure. The La_1-xBa_xMnO_3+δ based sensors showed excellent gas-sensing performance toward acetone (25–500 ppm) at 300 °C. It was also found that the La_0.80Ba_0.20MnO_3+δ sensor exhibited a fast response (≈25 s) and recovery time (≈15 s) in the presence of 100 ppm acetone gas, while the response value of the La_0.80Ba_0.20MnO_3+δ sensor to 500 ppm acetone reached 1350%. Moreover, these sensors also had good reproducibility and sensitivity to acetone. It reveals that Ba²⁺ as doping agent can partially convert Mn³⁺ to Mn⁴⁺, introducing numerous hole carriers into the p-type LaMnO_3+δ semiconductor and increasing the amount of chemisorbed oxygen ions on the surface, which can enhance the response of the sensor toward acetone. Moreover, this doping effect may also increase the hybridization of Mn 3d - O 2p orbits and double exchange interaction existing in the hybrid Mn³⁺/Mn⁴⁺ system, thereby promoting the carriers' conduction rate and gas sensing speed. These results suggest that the La_1-xBa_xMnO_3+δ perovskite-type structures can have large applicability in industrial acetone sensing.     

Influence of Ce addition on the structural,magnetic, and magnetocaloric properties in La0.7−xCexSr0.3MnO3 (0≤x≤0.3) ceramic compound

We report improvement in the magnetocaloric properties of Ce-doped lanthanum manganites. Polycrystalline La_0.7−xCe_xSr_0.30MnO₃ (0≤x≥0.3) samples were prepared using the conventional solid-state reaction method with phase purity and structure confirmed using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order ferromagnetic transition in parent sample and as well as in doped sample with Curie temperature decreasing progressively with increasing Ce-concentration from ~370 K for x=0.0 to 310 K for x=0.30. Magnetic entropy change (ΔS_M) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field dependent magnetization curves. A large ΔS_M associated with the ferromagnetic–paramagnetic transition in La_0.7−xCe_xSr_0.30MnO₃ samples has been observed. The value of ΔS_M was found to increase with Ce-doping up to x=0.15 and the highest value of 2.12 J kg⁻¹ K⁻¹ (at ΔH=2 T) was observed for La_0.55Ce_0.15Sr_0.30MnO₃ sample near the Curie temperature of 356 K. Also, improved relative cooling power of ~122 J kg⁻¹ was observed for the same sample. Due to the large magnetic entropy change and high Curie temperature, the La_0.55Ce_0.15Sr_0.30MnO₃ sample is suggested to be used as potential magnetic refrigerants for magnetic refrigeration technology above room temperature.     

Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment

High-density La_0.9-xSr_xK_0.1MnO₃ ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr²⁺ ions, substituting La³⁺ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K^?1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping.     

Effect of sulphur poisoning on perovskite catalysts prepared by flame-pyrolysis

ABO₃ perovskite-like catalysts are known to be sensitive to sulphur-containing compounds. Possible solutions to increase resistance to sulphur are represented by either catalyst bed protection with basic guards or catalyst doping with different transition or noble metals. In the present work La_(1−x)A^′_xCoO₃, La_(1−x)A^′_xMnO₃ and La_(1−x)A^′_xFeO₃, with A′ = Ce, Sr and x = 0, 0.1, 0.2, either pure or doped with noble metals (0.5 wt% Pt or Pd), were prepared in nano-powder form by flame-pyrolysis. All the catalysts were tested for the catalytic flameless combustion of methane, monitoring the activity by on-line mass spectrometry. The catalysts were then progressively deactivated in operando with a new procedure, consisting of repeated injection of some doses of tetrahydrothiophene (THT), usually employed as odorant in the natural gas grid, with continuous analysis of the transient response of the catalyst. The activity tests were then repeated on the poisoned catalyst. Different regenerative treatments were also tried, either in oxidising or reducing atmosphere.Among the unsubstituted samples, higher activity and better resistance to poisoning have been observed in general with manganites with respect to the corresponding formulations containing Co or Fe at the B-site. The worst catalyst showed LaFeO₃, from both the points of view of activity and of resistance to sulphur poisoning. La_0.9Sr_0.1MnO₃ showed, the best results, exhibiting very high activity and good resistance even after the addition of up to 8.4 mg of THT/g of catalyst. Interesting results were attained also by adding Sr to Co-based perovskites. Sr showed a first action by forcing Mn or Co in their highest oxidation state, but, in addition, it could also act as a sulphur guard, likely forming stable sulphates due to its basicity. Among noble metals, Pt doping proved beneficial in improving the activity of both the fresh and the poisoned catalyst.     

Evolution of structural,magnetic and magnetocaloric effect in TmFe1-xMnxO3 (x≤0.3)

The influence of Mn doping on structure, magnetic behaviors and magnetocaloric effect in TmFeO₃ polycrystalline ceramics has been explored. X-ray powder diffraction proves that TmFe_1-xMn_xO₃ (x ≤ 0.3) ceramics maintain an orthorhombic structure, and the space group is Pbnm. Compared with the original TmFeO₃ sample, structural parameters change slightly and magnetic properties are effectively tuned with the gradual substitution of Mn at Fe site. The spin reorientation temperature region shifts from 90.3 to 73.2 K for TmFeO₃ to 180.0–156.0 K for TmFe_0.7Mn_0.3O₃. Besides, for TmFe_1-xMn_xO₃ (x ≤ 0.3), the maximum magnetic entropy changes dependent on the Mn composition are 6.29 J/kg K, 6.56 J/kg K, 6.79 J/kg K and 7.22 J/kg K for 0–70 kOe, respectively. The refrigeration capacities are 159.3 J/kg, 168.9 J/kg, 176.7 J/kg and 184.4 J/kg, respectively. For a better assessing the magnetocaloric performance of TmFe_1-xMn_xO₃ (x ≤ 0.3), we have calculated the temperature average entropy change, refrigerant capacity and normalized refrigerant capacity, and their values become larger with increasing Mn doping. Our experimental results can provide valuable references for the application and development of RFeO₃ (R = rare earth) as multifunctional materials.     

A-site mixed-valence co-doping to optimize room-temperature TCR of polycrystalline La0.8K0.04Ca0.16-xSrxMnO3 ceramics

Herein, polycrystalline La_0.8K_0.04Ca_0.16-xSr_xMnO₃ ceramics (A-site = La, K, Ca and Sr, 0.00 ≤ x ≤ 0.16) are successfully synthesized via the sol-gel process and the influence of Sr content on microstructural and electrical transport properties is investigated in detail. The results reveal that the replacement of Ca-ions by Sr-ions resulted in a decreased resistivity and enhanced temperature coefficient of resistance (TCR) peak temperature (T_k). The influence of A-site mixed-valence co-doping, where A-site is occupied by monovalent alkali-metal, divalent alkaline-earth element and trivalent rare-earth element, on electrical transport properties can be explained by using different conduction mechanisms in different temperature regions. At optimal doping content of 0.12, peak TCR of the resistivity was found to be 12.04% K⁻¹ at 290.38 K, which is the best reported TCR for A-site mixed-valence co-doped perovskite manganese oxides. These results confirm that high room-temperature TCR values can be achieved by optimizing A-site mixed-valence co-doping and demonstrate the potential of polycrystalline La_0.8K_0.04Ca_0.04Sr_0.12MnO₃ ceramic in uncooling infrared bolometers.     

Electronic conductivity,oxygen permeability and thermal expansion of Sr0.7Ce0.3Mn1−xAlxO3−δ

The maximum solubility of aluminum cations in the perovskite lattice of Sr_0.7Ce_0.3Mn_1−xAl_xO_3−δ is approximately 15%. The incorporation of Al³⁺ increases oxygen ionic transport due to increasing oxygen nonstoichiometry, and decreases the tetragonal unit cell volume and thermal expansion at temperatures above 600 °C. The total conductivity of Sr_0.7Ce_0.3Mn_1−xAl_xO_3−δ (x = 0–0.2), predominantly electronic, decreases with aluminum additions and has an activation energy of 10.2–10.9 kJ/mol at 350–850 °C. Analysis of the electronic conduction and Seebeck coefficient of Sr_0.7Ce_0.3Mn_0.9Al_0.1O_3−δ, measured in the oxygen partial pressure range from 10⁻¹⁸ to 0.5 atm at 700–950 °C, revealed trends characteristic of broad-band semiconductors, such as temperature-independent mobility. The temperature dependence of the charge carrier concentration is weak, but exhibits a tendency to thermal excitation, whilst oxygen losses from the lattice have an opposite effect. The role of the latter factor becomes significant at temperatures above 800 °C and on reducing p(O₂) below 10⁻⁴ to 10⁻² atm. The oxygen permeability of dense Sr_0.7Ce_0.3Mn_1−xAl_xO_3−δ (x = 0–0.2) membranes, limited by both bulk ionic conduction and surface exchange, is substantially higher than that of (La, Sr)MnO₃-based materials used for solid oxide fuel cell cathodes. The average thermal expansion coefficients of Sr_0.7Ce_0.3Mn_1−xAl_xO_3−δ ceramics in air are (10.8–11.8) × 10⁻⁶ K⁻¹.     

Co-optimization of Na and K doping for improved room-temperature TCR of La0.7(Na0.3-xKx)MnO3 polycrystalline ceramics

Polycrystalline La_0.7(Na_0.3-xK_x)MnO₃ (LNKMO, x = 0.10, 0.15, 0.20, 0.25, and 0.26) ceramics were successfully compounded by adopting conventional sol-gel technology. The physical properties of as-prepared specimens were closely related to their morphology and internal structure, which were characterized and analyzed via X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Results confirmed that La⁺ ions located at A-sites in crystal lattice were partially substituted by doped Na⁺ and K⁺ ions, which resulted in rotation and distortion of MnO₆ octahedron. Lattice distortion was primary factor behind double exchange (DE) mechanism and Jahn-Teller (JT) effects. In addition, Na and K dopants altered relative amount of Mn³⁺ and Mn⁴⁺ ions, causing intensity variation in DE effect. These changes contributed to a decline in resistivity and an increase in peak resistance temperature (T_k) with increasing K doping level. Meanwhile, optimal temperature coefficient of resistance (TCR) value of LNKMO ceramics reached 8.48% K^?1 at 292.14 K when x = 0.25. This work reveals the mechanism of Na and K co-doping to optimize electrical transport properties of LNKMO manganese oxides and provides excellent material for the fabrication of uncooled infrared bolometers.     

Insights into the Reactivity of La1?xSrxMnO3 (x?=?0?÷?0.7) in High Temperature N2O Decomposition

Abstract  

In this paper a wide range of La_1−x Sr _x MnO₃ (x = 0–0.7) perovskites was synthesized by Pechini route, characterized by XRD (including high temperature measurements), XPS, differential dissolution phase analysis, TPR H₂, oxygen exchange and tested in N₂O decomposition at 900 °C. At low degree of Sr substitution for La (x ≤ 0.3), high catalytic activity was found for perovskites with hexagonal structure (x = 0.1–0.2) and can be related to fast oxygen mobility caused by the lattice disordering during polymorphic phase transition from the hexagonal to cubic structure. For multiphase samples (x > 0.3) increase of activity and oxygen mobility can be attributed to the formation of the layer-structured perovskite–LaSrMnO₄ on the surface.