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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Optical characterization of ZnO nanomaterial with praseodymium ions

ZnO nanomaterial with praseodymium ions was prepared by chemical synthesis method. The ZnO nanomaterial was characterized by XRD, SEM and TEM. Their absorption in UV-VIS/NIR regions was measured at room temperature. The experimental oscillator strengths were calculated from the areas under the absorption bands. Eight absorption bands have been observed. From these spectral data various energy interaction parameters like Slater–Condon, Lande, Racah, Nephelauxetic ratio and bonding parameters have been computed. Judd-Ofelt analysis has been carried out using the absorption spectra to evaluate the radiative properties for luminescent levels of the praseodymium ion and discussed. The observed nano particle size is 2nm.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High Pressure Synthesis of Pr 2 O 5 – A Unique Lanthanoid(IV) Oxide Peroxide

Abstract Reacting praseodymium(IV) oxide with oxygen at 27 GPa in a diamond anvil cell yielded the oxide peroxide Pr 2 IV (O 2 )O 3 , which was characterized by single crystal X‐ray diffraction on multi‐grain samples, Raman spectroscopy and quantum theoretical calculations at various pressure points. The presence of tetravalent praseodymium ions is supported by electronic structure calculations, showing a band gap of ca. 1.2 eV, which is consistent with the anticipated chemical model of an ionic solid. Pr 2 (O 2 )O 3 thus far represents the most oxygen rich phase of any binary compound of a lanthanoid and oxygen and is the first example of a peroxide anion next to Pr 4+ . Additionally, these results demonstrate that instead of oxidizing the praseodymium ions past their +IV oxidation state, oxygen undergoes a comproportionation to form peroxide anions. Direct oxidation of the oxide anions by Pr 4+ ‐ions was ruled out by a control experiment in argon instead of oxygen, where no oxidation of oxide ions was observed.

Chemistry↗
DOE OSTI2018

Spectral Characteristics and Thermal Quenching of Luminescence in Rb{sub 0.993}Pr{sub 0.007}Pb{sub 2}Br{sub 5} and Rb{sub 0.993}Pr{sub 0.007}Pb{sub 2}Cl{sub 2.5}Br{sub 2.5} Crystals

Crystals with the compositions Rb{sub 0.993}Pr{sub 0.007}Pb{sub 2}Br{sub 5} and Rb{sub 0.993}Pr{sub 0.007}Pb{sub 2}Cl{sub 2.5}Br{sub 2.5} have been grown by the Bridgman method, and the absorption, luminescence excitation, and photoluminescence spectra of these materials in the case of the Stokes mechanism of optical excitation in the blue spectral region have been analyzed. The intensity of the visible luminescence bands of the Pr{sup 3+} praseodymium ions has been shown to depend on the nature of the nearest neighbor atoms in their crystalline environment. This effect is tentatively attributed to changes in the probability of radiative transitions in the rare-earth ion. The temperature dependences of emission intensity obtained for the crystals demonstrate that the contributions of nonradiative recombination channels depend on the transition, which also leads to changes in the emission color of the compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2018

Mid-infrared Spectroscopy of Pr-Doped Materials

Solid state lanthanide doped lasers primarily operate in the ultraviolet, visible, near infrared and short-wavelength infrared out to around 2.1 μm. At longer wavelengths, the transitions in conventional oxide crystal and glass materials become susceptible to multiphonon quenching due to their relatively large phonon energy. The use of low phonon materials can minimize the nonradiative quenching, opening up possibilities for solid state lanthanide lasers operating in the mid-infrared (MIR). This provides motivation to study the spectroscopy of lanthanide ions in bromide, chloride and fluoride materials, which have relatively low phonon energies. In this article, the MIR spectroscopy or praseodymium ions in five different host materials is studied, specifically KPb2Br5 (KPB), LaF3, KYF4 (KYF), BaY2F8 (BYF) and YLiF4 (YLF) host crystals. The MIR emission cross sections have been measured from 3 to 6 μm and reciprocity of absorption and emission is utilized to validate the results. The lifetime dynamics in the MIR are covered for various pump and emission wavelengths. Results are also presented on MIR emission from 6.5 to 8.5 μm in a Pr: KPB crystal, which, to the best of the authors knowledge, is the first such measurement of luminescence in this wavelength range that has been published.

Brian M Walsh↗
DOE OSTI2021

Active Tuning of Optical Constants in the Visible–UV: Praseodymium-Doped Ceria—a Model Mixed Ionic–Electronic Conductor

Mixed ionic-electronic conductors offer chemical and electrical means for active tuning of their optical constants, e.g. with variations in oxygen non-stoichiometry in Pr 0.1 Ce 0.9 O 2-δ , enabling implementation of adaptive thin film optical devices. Here, we demonstrate in-situ chemo-tuning of the extinction coefficient in Pr 0.1 Ce 0.9 O 2-δ at elevated temperatures and provide a tuning model that treats the interdependence of mobile oxygen vacancies and small polarons coupled to variations in optically active praseodymium ions. Further, a new means for electro-tuning of the optical constants of mixed ionic-electronic conductors was demonstrated experimentally and modeled for Pr 0.1 Ce 0.9 O 2-δ thin films deposited on grid-like electrode structures. Modeling of non-steady state optical transmittance modulations in the latter allows for estimation of oxygen vacancy mobility that determines the switching speed of the device. Quenched-in values of nr and k to room temperature become nonvolatile, providing a modulation range in the extinction coefficient of Δk ~0.1 (change of ~800%) and in the refractive index of Δn r ~0.1 (relative to initial n r of ~2.35). Key figures of merit including, transmission optical modulation of ~0.04 per 1 mV nm -1 , switching energy per area of 670 pJ μm -2 and switching times of seconds, were demonstrated, with further improvements possible.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Luminescence improvement in Pr{sup 3+} and Gd{sup 3+} activated Sr{sub 2}Mg(BO{sub 3}){sub 2} inorganic phosphor

Highlights: • Sr{sub 2}Mg(BO{sub 3}){sub 2} doped Gd{sup 3+} and Pr{sup 3+} have been synthesized by solution combustion synthesis technique. • Effect of doping concentration of Gd{sup 3+} and Pr{sup 3+} on the luminescence of synthesized material is discussed. • Effect of charge compensation by Li{sup +}, Na{sup +} and K{sup +} on emission intensity is studied in detail. • Efficient energy transfer from Pr{sup 3+} to Gd{sup 3+} in Sr{sub 2}Mg(BO{sub 3}){sub 2} was observed. • Optimum concentration and critical transfer distance for optimum concentration have been determined. - Abstract: The photoluminescence properties of (Sr{sub 1−x}Pr{sub x}){sub 2}Mg(BO{sub 3}){sub 2}; (Sr{sub 1−2x}Pr{sub x}M{sub x}){sub 2}Mg(BO{sub 3}){sub 2,} (M = Li, Na, K); (Sr{sub 1−x}Gd{sub x}){sub 2}Mg(BO{sub 3}){sub 2}; (Sr{sub 1−2x}Gd{sub x}M{sub x}){sub 2}Mg(BO{sub 3}){sub 2}, (M = Li, Na, K) and (Sr{sub 1−4x}Pr{sub x}Gd{sub x}Na{sub 2x}){sub 2}Mg(BO{sub 3}){sub 2} inorganic phosphors prepared by solution combustion synthesis technique are discussed. The structure of the prepared phosphor characterized using Thermogravimetric–differential thermal analysis, X-ray diffraction and fourier transform-infrared. Scanning electron microscopy images of the prepared materials show irregular grains with agglomerate phenomena. Photoluminescence properties were studied at room temperature. Optimum concentration and critical transfer distance of the synthesized phosphors were determined.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Single crystal growth and variation of thermodynamic and magnetic properties of Pr1−xLaxAlO3 (x = 0, 0.8)

Highlights: • The perovskite Pr{sub (1-x)}La{sub (x)}AlO{sub 3} was grown by two different protocols to control the P{sup 4+} concentration. • Low temperature magnetic properties in bulk single crystals are sensitive to annealing protocols. • Post growth annealing in a reducing atmosphere leads to closest Pr{sub 0.2}La{sub 0.8}AlO{sub 3} stoichiometry. • A possible new magnetic transition for single crystal PrAlO{sub 3} is observed at 6 K. - Abstract: Two approaches to using optical floating zone (OFZ) technique for single crystal growth of the perovskite Pr{sub 1−x}La{sub x}AlO{sub 3} are discussed, along with the influence on the physical properties of the resulting single crystals due to oxidizing and reducing post anneals. In method one (M1) we used pre-reduced Pr{sub 2}O{sub 3} powder starting material, while in the other method, M2, we employed an argon 5% hydrogen reducing environment during the floating zone single crystal growth. Magnetic susceptibility of the low temperature monoclinic phase of Pr{sub 0.2}La{sub 0.8}AlO{sub 3} is shown to be sensitive to the precise annealing protocol followed. For the post-growth reduced single crystal the magnetic susceptibility is flat across the R-3c to C2/m structural transition, whereas the oxidized and as-grown samples display a sharp upturn and downturn, respectively. We attribute the low temperature susceptibility differences to relative proportions of Pr{sup 3+} and Pr{sup 4+}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Radiative Lifetimes of the Energy Levels of Palladium-like Ions Pr XIV and Nd XV

Radiative lifetimes for the 4d{sup 9}4f, 4d{sup 9}5p, 4d{sup 9}5d, and 4d{sup 9}6s levels in the spectra of palladium-like ions Pr XIV and Nd XV are calculated in the electric-dipole approximation by the intermediate coupling semiempirical method with the use of experimental energy levels available in the literature. The radial integrals of transitions necessary for calculating absolute values of transition probabilities are obtained in the length form with Hartree–Fock functions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Electronic and Magnetic States of Pr and Mn in the Pr{sub 1–x}Sr{sub x}MnO{sub 3} Films Studied by XANES and XMCD Spectroscopy

The spectral dependences of X-ray absorption near-edge spectroscopy (XANES) and X-ray magnetic circular dichroism (XMCD) and the field dependences of XMCD near the K edge of Mn and the L{sub 2,3} edges of Pr in the Pr{sub 0.8}Sr{sub 0.2}MnO{sub 3} and Pr{sub 0.6}Sr{sub 0.4}MnO{sub 3} films at T = 90 K are studied. The spectral dependences point to a mixed valence state of Mn and Pr in the films. It is found that, as compared to XANES, XMCD is more sensitive to the valence state of Pr{sup 4+}. The field dependences of XMCD point to ferromagnetic behavior of Mn ions and the Van Vleck paramagnetism of Pr ions, which makes a significant contribution to the total magnetization of the films. It is shown that as the Sr concentration increases, the XMCD intensity at the K edge of Mn increases, which indicates a growth of the total magnetic moment of the film due to an increase in the 4p–3d hybridization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Luminescence of Pr{sup 3+} and Nd{sup 3+} Ions in Double Molybdates

The optical spectra of samples of double zirconium molybdates activated by rare-earth Pr{sup 3+} and Nd{sup 3+} ions are studied. The presence of bands corresponding to the 4f–4f transitions of Pr{sup 3+} and Nd{sup 3+} trivalent ions in the absorption, excitation, and luminescence spectra is shown. A strong dependence of the luminescence intensity of Pr{sup 3+} ions on temperature is revealed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effect of the introduction of oxide ion vacancies into cubic fluorite-type rare earth oxides on the NO decomposition catalysis

Cubic fluorite-type solid solutions based on Pr{sub 6}O{sub 11} and CeO{sub 2} were synthesized and oxide anion vacancies were intentionally introduced into the cubic fluorite-type lattice through the charge compensating mechanism by Mg{sup 2+} and/or Ca{sup 2+} doping into their lattices. The oxide anion vacancies bring about positive effect on NO decomposition catalysis. The reason for the increase in the catalytic activity was attributed to defect fluorite-type structures close to the C-type cubic one, because C-type cubic rare earth oxides, in which one-quarter of the oxygen atoms in the fluorite-type structure are removed, show high NO decomposition activity. In particular, the positive effect of the formation of oxide anion vacancies was significant for Pr{sub 6}O{sub 11} and its solid solutions, because the molar volume of Pr{sub 6}O{sub 11} is larger than that of CeO{sub 2}, and Pr{sub 6}O{sub 11} contains Pr{sup 3+} as well as Pr{sup 4+} and thereby a small amount of oxide anion vacancies exist inherently in the lattice. - Graphical abstract: Oxide anion vacancies intentionally introduced into the cubic fluorite-type lattice bring about positive effect on NO decomposition catalysis. - Highlights: • Cubic fluorite-type solid solutions were synthesized. • Oxide anion vacancies were intentionally introduced into the cubic fluorite-type lattice. • The oxide anion vacancies bring about positive effect on NO decomposition catalysis. • The activity was enhanced by making the structure close to the C-type cubic one.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Modifying the hygroscopic property of La{sub 2}O{sub 3} by Pr, Sm and Nd doping

Combustion synthesized La{sub 2}O{sub 3}, La{sub 2-2x}Pr{sub 2x}O{sub 3} (x = 0.025–0.30), La{sub 2-2x}Nd{sub 2x}O{sub 3} (x = 0.025–0.50), La{sub 2-2x}Sm{sub 2x}O{sub 3} (x = 0.025–0.30) and their subsequently formed hydroxide phases were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The hydroxylation reaction (hygroscopic property) of oxides in an open atmosphere was monitored by X-ray diffraction (XRD). All of these oxides hydroxylate to form stable hydroxides at room temperature upon exposure to open atmosphere for certain interval of time. La{sub 2}O{sub 3} shows rapid hydroxylation reaction as compared to other oxides (La{sub 2-2x}M{sub 2x}O{sub 3}, M = Pr, Nd, Sm). It is observed that La{sub 2-2x}Pr{sub 2x}O{sub 3} shows the slowest hydroxylation reaction compared to La{sub 2-2x}Nd{sub 2x}O{sub 3} and La{sub 2-2x}Sm{sub 2x}O{sub 3}. Further, as the concentration of dopant ion concentration increases in each La{sub 2-2x}Pr{sub 2x}O{sub 3} (x = 0.05, 0.15 and 0.30), La{sub 2-2x}Nd{sub 2x}O{sub 3} (x = 0.05, 0.15, 0.30 and 0.50) and La{sub 2-2x}Sm{sub 2x}O{sub 3} (x = 0.05, 0.15 and 0.30), the hydroxylation reaction becomes slower consecutively. Overall, 30% Pr doped La{sub 2}O{sub 3} (La{sub 1.40}Pr{sub 0.60}O{sub 3}) shows the highest stability (slowest rate of hydroxylation) in open atmosphere at room temperature. - Graphical abstract: Compared to La{sub 2}O{sub 3} (20 h), La{sub 1.40}Nd{sub 0.60}O{sub 3}, La{sub 1.40}Sm{sub 0.60}O{sub 3} and La{sub 1.40}Pr{sub 0.60}O{sub 3} take much more time to convert into hydroxide with conversion times of 100, 150 and 230 h respectively. Display Omitted - Highlights: • La{sub 2}O{sub 3}, La{sub 2-2x}Pr{sub 2x}O{sub 3} (x = 0.025–0.30), La{sub 2-2x}Nd{sub 2x}O{sub 3} (x = 0.025–0.50) and La{sub 2-2x}Sm{sub 2x}O{sub 3} (x = 0.025–0.30) were synthesized by solution combustion method. • All the oxides completely convert into their hydroxide phase in open atmosphere. • The consistent peak shifting in the XRD toward the higher 2θ value is observed due to substitution of larger ions (La{sup 3+}) by smaller ions (Pr{sup 3+}/Pr{sup 4+}, Nd{sup 3+}and Sm{sup 3+}). • Stability of La{sub 2}O{sub 3} increases with increasing the dopant concentration. • La{sub 1.40}Pr{sub 0.60}O{sub 3} shows the highest stability in open atmosphere.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural, optical and dielectric properties of Ce{sup 3+}, Pr{sup 3+}, Nd{sup 3+} doped LaF{sub 3} hexagonal nanoparticles

Well dispersed, elongated and hexagonal LaF{sub 3}: Ce{sup 3+}, Pr{sup 3+}, Nd{sup 3+} nanocrystals have been synthesized by microwave assisted technique. X-ray diffraction (XRD) studies indicates the formation of nanocrystals with unit cell parameters a = b = 7.144 A{sup 0}, c = 7.281 A{sup 0}, (c/a = 1.019) and unit cell volume of 321.86 (A{sup 0}){sup 3} of average crystallite size 21 nm have been traced by from XRD analysis and it is close agreement with transmission electron microscope (TEM) analysis. Ultra-violet (UV) absorption spectrum shows an edge at 250 nm indicating presence of wide transparency window region between 200 nm-800 nm. Fundamental groups have been observed in the Fourier transformation infrared (FTIR) and FT-Raman spectra. The blue luminescent properties of the nanoparticles were investigated by excitation and emission spectra. Room temperature Electrical and dielectric properties were studied for the synthesized nanocrystals the values of conductivity & resistivity is found to be in the order of 10{sup −6} Scm{sup −1} and resistivity 10{sup 5} Ω cm. Low dielectric constant value was observed in the LaF{sub 3}: Ce{sup 3+}, Pr{sup 3+}, and Nd{sup 3+} nanocrystals at high frequency indicating its suitability for electro optics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Manipulating the ferromagnetism in narrow-bandwidth Pr{sub 1-x}Ca{sub x}MnO{sub 3} (0 ≤ x ≤ 0.6) by means of the Mn-Ru t{sub 2g} ferromagnetic super-exchanges

The concurrent ferromagnetic and metal-insulator transitions via the double-exchange route and electronic phase separation scenario represent the core ingredients of the physics of manganites. In this work, a Ca{sup 2+} and Ru{sup 4+} co-substitution of Pr{sup 3+} and Mn{sup 3+} in narrow-bandwidth and insulating PrMnO{sub 3}, namely, Pr{sub 1-x}Ca{sub x}Mn{sub 1-x}Ru{sub x}O{sub 3} (PCMRO, x ≤ 0.6), is carried out in order to investigate an alternative approach to effectively manipulate the ferromagnetism of PrMnO{sub 3}-based manganites. It is revealed that PCMRO over the whole substitution range is homogeneous solid solution with increased lattice distortion. The preference of Ru{sup 4+} valence state and the absence of Mn{sup 4+} valence state disable the Mn{sup 3+}-Mn{sup 4+} e{sub g}-orbital double-exchange, and the random occupation of Ru{sup 4+} in the lattice excludes the charge ordering and electronic phase separation. While all these consequences should favor antiferromagnetic insulating states, nevertheless, a high-temperature ferromagnetic transition is triggered by the co-substitution and the magnetization can reach up to ∼1.0 μ{sub B}/f.u. at x ∼ 0.2–0.3, much bigger than the moment (<0.1 μ{sub B}/f.u.) of Pr{sub 1−x}Ca{sub x}MnO{sub 3} in the weak ferromagnetic insulator state. It is suggested that this strong ferromagnetism is substantially ascribed to the Mn{sup 3+}-Ru{sup 4+} t{sub 2g}-orbital ferromagnetic super-exchange, and a simple geometric network illustration of the magnetism and electrical transport is presented.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Variation in plasmonic (electronic) spectral parameters of Pr (III) and Nd (III) with varied concentration of moderators

It is said that the -4f shells behave as core and are least perturbed by changes around metal ion surrounding. However, there are evidences that-4f shells partially involved in direct moderator interaction. A systematic investigation on the plasmonic (electronic) spectral studies of some Rare Earths[RE(III).Mod] where, RE(III) = Pr(III),Nd(III) and Mod(moderator) = Y(III),La(III),Gd(III) and Lu(III), increased moderator concentration from 0.01 mol dm{sup −3} to 0.025 mol dm{sup −3} keeping the metal ion concentration at 0.01mol dm{sup −3} have been carried out. Variations in oscillator strengths (f), Judd-Ofelt parameters (T{sub λ}),inter-electronic repulsion Racah parameters (δE{sup k}),nephelauxetic ratio (β), radiative parameters (S{sub ED},A{sub T},β{sub R},T{sub R}). The values of oscillator strengths and Judd-Ofelt parameters have been discussed in the light of coordination number of RE(III) metal ions, denticity and basicity of the moderators. The [RE(III).Mod] bonding pattern has been studies in the light of the change in Racah parameters and nephelauxetic ratio.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Enhanced Pr{sup 3+} photoluminescence by energy transfer in SrF{sub 2} : Eu{sup 2+}, Pr{sup 3+} phosphor

Efficient energy transfer was demonstrated in the SrF{sub 2} : Eu{sup 2+}, Pr{sup 3+} phosphor synthesized by the co-precipitation method. Results obtained with X-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray spectroscopy (XPS), photoluminescence (PL) and decay curves proposed the UV-Vis energy transfer process. The energy transfer process between the Eu{sup 2+} and Pr{sup 3+} ions in SrF{sub 2} was investigated to evaluate the potential of the Eu{sup 2+} ion as a sensitizer for the Pr{sup 3+} ion. The results proposed that Eu{sup 2+} could be a good sensitizer for absorbing the UV photons and efficiently enhancing the Pr{sup 3+} emission intensity. The energy transfer process was effective until concentration quenching for the Pr{sup 3+} ions occurred. The concentration quenching was attributed to cross-relaxation between the Pr{sup 3+} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Controllable synthesis and tunable luminescence of glass ceramic containing Mn{sup 2+}:ZnAl{sub 2}O{sub 4} and Pr{sup 3+}:YF{sub 3} nano-crystals

Highlights: • Glass ceramic containing ZnAl{sub 2}O{sub 4} and YF{sub 3} nano-crystals is fabricated. • Mn{sup 2+} and Pr{sup 3+} are selectively incorporated into ZnAl{sub 2}O{sub 4} and YF{sub 3}, respectively. • The luminescence color can be tuned by adjusting the excitation wavelength. - Abstract: Glass ceramic containing spinel ZnAl{sub 2}O{sub 4}:Mn{sup 2+} and orthorhombic YF{sub 3}:Pr{sup 3+} nano-crystals has been successfully prepared by a melt-quenching technique. X-ray diffraction and transmission electron microscopy demonstrated that two nano-phases, i.e. ZnAl{sub 2}O{sub 4} and YF{sub 3}, were homogeneously distributed among the glass matrix. Importantly, the selective incorporation of Pr{sup 3+} ions into the Y{sup 3+} nine-fold coordinated sites of YF{sub 3} and the segregation of Mn{sup 2+} dopants in the Zn{sup 2+} tetrahedral sites of ZnAl{sub 2}O{sub 4} were confirmed based on the excitation/emission spectra and the crystal field calculation. Under blue light excitation, both Pr{sup 3+} and Mn{sup 2+} in the glass ceramic can be simultaneously excited, and emit red and green luminescence, respectively, owing to the suppression of energy transfer between them. The luminescence color of the obtained glass ceramic can be easily tuned by adjusting the excitation wavelength. These results indicate the potential application of the glass ceramic as converting phosphor to generate white-light after coupling with the blue LED chip.

36 MATERIALS SCIENCE↗
DOE OSTI2016

High-pressure synthesis and relationship between A-site ordering and local structure of multicomponent perovskites (Ln{sub 0.25}Mn{sub 0.75})(Al{sub 0.25}Ti{sub 0.75})O{sub 3}, Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Y

ABSTRACT: The synthesis of multicomponent perovskites (Ln{sub 0.25}Mn{sub 0.75})(Al{sub 0.25}Ti{sub 0.75})O{sub 3} (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Y) have been investigated using a high-pressure and high-temperature (6 GPa, 1175 °C) technique. When Ln{sup 3+} is larger La{sup 3+}, Pr{sup 3+}, Nd{sup 3+}, the A-site ordered perovskites, LnMn{sub 3}(Al{sub 0.25}Ti{sub 0.75}){sub 4}O{sub 12} in Im-3, have been successfully synthesized. The A-site partially disordered one, (Sm{sub 0.80}Mn{sub 0.20})(Sm{sub 0.07}Mn{sub 0.93}){sub 3}(Al{sub 0.25}Ti{sub 0.75}){sub 4}O{sub 12} is also obtained. In the case of smaller Gd{sup 3+}, Tb{sup 3+}, Dy{sup 3+}, we have obtained no single phase but two decomposed perovskite phases. When Ln{sup 3+} is much smaller Y{sup 3+}, it is crystallized as an A-site disorder one in Pnma. The Rietveld structural refinements of the A-site ordered and partially disordered perovskites indicate that the tilting of (Al/Ti)O{sub 6} octahedrons for the A-site ions ordering is correlated with the (Al/Ti)–O and Ln–O bond lengths to optimize the coordination of the A- and A′-sites. The phase stability of the A-site ordered perovskites is discussed from the viewpoint of this correlation. - Graphical abstract: Ln{sup 3+} (VIII) ionic radius dependence of BO{sub 6} octahedron tilt angle and A/B–O distance of Im-3 perovskites (Ln{sub 0.25}Mn{sub 0.75})(Al{sub 0.25}Ti{sub 0.75})O{sub 3} (Ln=La-Sm).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗