Oxygen stoichiometry and structural properties of La1 – xAxMnO3 ± δ (A = Ca or Sr and 0 ≤ x ≤ 1)

Rørmark, Lisbeth; Wiik, Kjell; Stølen, Svein; Grande, Tor

doi:10.1039/b103510j

Cited by 124 publications

(146 citation statements)

References 40 publications

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“…To have a higher temporal and also spatial resolution than with scanning probe microscopy we used low energy electron microscopy (LEEM). Here, the electron probe-beam can be used to charge the surface of an insulating sample and First we calculate the strain dependence of oxygen vacancy formation, and find that tensile epitaxial strain promotes the formation of oxygen vacancies on the equatorial site, with 2% strain increasing the vacancy concentration by one order of magnitude at room temperature, consistent with previously reported off-stoichiometry 15 . Figure 5a shows the environment of such a strain-promoted oxygen vacancy.…”

supporting

confidence: 86%

Strain-induced coupling of electrical polarization and structural defects in SrMnO3 films

et al. 2015

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Local perturbations in complex oxides such as domain walls 1,2 , strain 3,4 and defects 5,6 are of interest because they can modify the conduction or the dielectric and magnetic response and even promote phase transitions. Here we show that the interaction between different types of local perturbations in oxide thin films is an additional source of functionality. Taking SrMnO 3 as a model system, we use nonlinear optics to verify the theoretical prediction that strain induces a polar phase, and density functional theory to show that strain simultaneously increases the concentration of oxygen vacancies. These vacancies couple to the polar domain walls where they establish an electrostatic barrier to electron migration. The result 2 is a state with locally structured room-temperature conductivity consisting of conducting nanosized polar domains encased by insulating domain boundaries, which we resolve using scanning probe microscopy. Our "nanocapacitor" domains can be individually charged, suggesting stable capacitance nanobits with a potential for information storage technology.At first we verify the occurrence of strain-induced polar order in SrMnO 3 thin films.Motivated by the search for novel multiferroic materials, which combine magnetic and ferroelectric orders in the same phase, density functional theory (DFT) predicted the occurrence of ferroelectricity in the perovskite-structure alkaline-earth manganites at larger-than-equilibrium lattice parameters 7,8,9 . For bulk SrMnO 3 this prediction was confirmed by partial substitution of Sr by Ba which induces negative chemical pressure and leads to a polar state 10 . According to DFT, epitaxial SrMnO 3 films should develop a polarisation along one of the pseudocubic <110> axes under >1% epitaxial tensile strain 8 .20-nm films of single-phase SrMnO 3 were grown using pulsed laser deposition on (001)-oriented (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT) with 1.7% tensile strain (see Methods). We characterised the strain state of the films using scanning transmission electron microscopy (STEM) and X-ray and electron diffraction. Figure 1a shows a cross-sectional STEM image evidencing the high quality of the films on the atomic scale with a sharp SrMnO 3 /LSAT (001) interface. The reciprocal space map in Fig. 1a verifies that the films are tetragonal and coherently strained. The electron diffraction In the anisotropy plot in Fig. 1c we present the optical polarisation analysis of the SHG signal obtained on a test area of 0.1 mm 2 . We fitted the angular dependence of the SHG signal by assuming a distribution of four polar domain states denoted as P 1+ , P 1− , P 2+ , P 2− . The indices refer to the orientation of the polar axis according to 1 ± ↔ ±[110] and 2 ± ↔ ±[1 10], see Fig. 1c. The coincidence of the measured data and the fit is excellent with a fitted ratio r = P 1 /P 2 = 0.53 in the population of P 1 -and P 2 -type domain states (r varied between different test areas). In contrast, fits assuming a polarisation along the[100] and [010] directions failed. We co...

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confidence: 86%

Strain-induced coupling of electrical polarization and structural defects in SrMnO3 films

et al. 2015

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“…When heating in air, stoichiometry CaMnO 3 with orthorhombic structure at room temperature lost oxygen forming the nonstoichiometric CaMnO 3-and transforms to tetragonal and subsequently to cubic symmetry structure at 869 ∘ C and 913 ∘ C [31,[45][46][47]. This transition would happen at lower temperatures in our experiment since the particles were heated in 5% O 2 in N 2 under a much lower oxygen partial pressure compared to air.…”

Section: Discussionmentioning

confidence: 87%

Examination of Perovskite Structure CaMnO_3-δwith MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

Jing

Mattisson

Leion

et al. 2013

International Journal of Chemical Engineering

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Perovskite structure oxygen carriers with the general formula CaMn x Mg 1-x O 3-were spray-dried and examined in a batch fluidized bed reactor. The CLOU behavior, reactivity towards methane, and syngas were investigated at temperature 900 ∘ C to 1050 ∘ C. All particles showed CLOU behavior at these temperatures. For experiments with methane, a bed mass corresponding to 57 kg/MW was used in the reactor, and the average CH 4 to CO 2 conversion was above 97% for most materials. Full syngas conversion was achieved for all materials utilizing a bed mass corresponding to 178 kg/MW. SEM/EDX and XRD confirmed the presence of MgO in the fresh and used samples, indicating that the Mg cation is not incorporated into the perovskite structure and the active compound is likely pure CaMnO 3-. The very high reactivity with fuel gases, comparable to that of baseline oxygen carriers of NiO, makes these perovskite particles highly interesting for commercial CLC application. Contrary to NiO, oxygen carriers based on CaMnO 3-have no thermodynamic limitations for methane oxidation to CO 2 and H 2 O, not to mention that the materials are environmentally friendly and can utilize much cheaper raw materials for production. The physical properties, crystalline phases, and morphology information were also determined in this work.

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“…The tetragonal phase is known to occupy a relatively small region in the p O 2 -Т-δ phase diagram between the low-temperature orthorhombic and high-temperature cubic phases [15]. Consequently, the available experimental data for the tetragonal structure are quite scarce [17].…”

Section: Partial Molar Enthalpy and Entropy Of Oxygenmentioning

confidence: 99%

“…At near atmospheric or lower pressures, alkali-earth manganites are oxygen deficient, and it is widely accepted that electrical neutrality of the crystalline lattice in, e.g., СаMnO 3−δ , is entirely maintained due to partial reduction of manganese cations, Mn 4+ → Mn 3+ [15]. The respective p O 2 -Т-δ diagram for СаMnO 3−δ was obtained in [16].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of oxygen in CaMnO3 − δ

Goldyreva

Леонидов

Патракеев

et al. 2013

J Solid State Electrochem

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The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO 3−δ . It is shown that along with the oxygen exchange reaction, thermal excitation of Mn 4+ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn 3+ cations.

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Oxygen stoichiometry and structural properties of La1 – xAxMnO3 ± δ (A = Ca or Sr and 0 ≤ x ≤ 1)

Cited by 124 publications

References 40 publications

Strain-induced coupling of electrical polarization and structural defects in SrMnO3 films

Strain-induced coupling of electrical polarization and structural defects in SrMnO3 films

Examination of Perovskite Structure CaMnO_3-δwith MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

Thermodynamics of oxygen in CaMnO3 − δ

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Oxygen stoichiometry and structural properties of La1 – xAxMnO3 ± δ (A = Ca or Sr and 0 ≤ x ≤ 1)

Cited by 124 publications

References 40 publications

Strain-induced coupling of electrical polarization and structural defects in SrMnO3 films

Strain-induced coupling of electrical polarization and structural defects in SrMnO3 films

Examination of Perovskite Structure CaMnO3-δwith MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

Thermodynamics of oxygen in CaMnO3 − δ

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Examination of Perovskite Structure CaMnO_3-δwith MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas