Thermogalvanic power and fast ion conduction in δ-Bi2O3 and δ-(Bi2O3)1−x(R2O3)x with R = Y, Tb---Lu

The thermogalvanic power (Seebeck coefficient) of O^2- conducting δ-Bi₂O₃ and δ-(Bi₂O₃)_1−x(Y₂O₃)_x has been measured directly as a function of temperature and partial oxygen pressure in N₂---O₂ mixtures. The of δ-(Bi₂O₃)_0.75(R₂O₃)_0.25 with R = Tb---Lu was indirectly determined using an isothermal concentration cell technique. Except for pure δ-Bi₂O₃, the heat of transport is much smaller than the activation energy for O^2- conduction for all materials. The vibrational freedom of O²⁻ ions in all δ-stabilized materials is reflected in their IR spectra at room temperature. Two prototypes of a thermogalvanic P_O2 meter were tested.     

Lithium ion conductive glass–ceramics with Li3Fe2(PO4)3 and YAG laser-induced local crystallization in lithium iron phosphate glasses

The glasses with the composition of 37.5Li₂O–(25 − x)Fe₂O₃–xNb₂O₅–37.5P₂O₅ (mol%) (x = 5,10,15) are prepared, and it is found that the addition of Nb₂O₅ is effective for the glass formation in the lithium iron phosphate system. The glass–ceramics consisting of Nasicon-type Li₃Fe₂(PO₄)₃ crystals with an orthorhombic structure are developed through conventional crystallization in an electric furnace, showing electrical conductivities of 3 × 10^− 6 Scm^− 1 at room temperature and the activation energies of 0.48 eV (x = 5) and 0.51 eV (x = 10) for Li⁺ ion conduction in the temperature range of 30–200 °C. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with powers of 0.14–0.30 W and a scanning speed of 10 μm/s is irradiated onto the surface of the glasses, and the formation of Li₃Fe₂(PO₄)₃ crystals is confirmed from XRD analyses and micro-Raman scattering spectra. The crystallization of the precursor glasses is considered as new route for the fabrication of Li₃Fe₂(PO₄)₃ crystals being candidates for use as electrolyte materials in lithium ion secondary batteries.     

Bond-Shift Rearrangement in Solid Li3P7(Monoglyme)3: A P MAS NMR Study

The ³¹P MAS NMR spectrum of solid Li₃P₇(monoglyme)₃ has been reinvestigated over a wide temperature range (−70 to +77°C) and under conditions of better resolution (Larmor frequency of 162 MHz and spinning rate of 30 kHz) than previously measured (121 MHz and 13 kHz). At low temperatures three spinning sideband (ssb) manifolds are observed: a singlet (centered at −45 ppm relative to 85% H₃PO₄) due to the apical atom (A) of the P₇-cage trianion; a 1 : 1 : 1 triplet (at −110, −117, and −124.5 ppm) due to the negatively charged equatorial (E) atoms, and a one to two doublet (at −161 and −168.5 ppm) due to the basal (B) atoms. These results are consistent with the P₇ cage having nearly, but not perfect, C_3v symmetry. The compound appears to be well ordered in the solid state with very little structural dispersity. On heating, the NMR lines broaden and eventually coalesce into a single ssb manifold. This behavior is ascribed to bond-shift rearrangement similar to the Cope rearrangement in bullvalene. A MAS 2D exchange experiment and a quantitative analysis of the 1D NMR lineshapes indicate that, unlike in solution where the rearrangement involves a single bond shift at a time, in the solid the process involves a succession of two bond shifts: The first leads to an intermediate species in which the rearranged P₇ cage is inverted, while in the subsequent step a second bond shift takes place that also restores the original orientation of the cage in the lattice. The overall effect of the double bond shift is equivalent to cyclic permutation of the phosphorus atoms within the five member rings of the P₇-cage. The quantitative analysis of the dynamic lineshapes shows that this cyclic permutation proceeds at a different rate in one ring (k_d¹) than in the other two (k_d^2,3). The kinetic parameters for these processes are E_a¹=18.7 kJ/mol, E_a^2,3=58.0 kJ/mol, k_d¹(17°C)=k_d^2,3(17°C)=10⁴ s⁻¹. No indications for independent threefold molecular jumps of the P₇ cage were found.     

Line strength measurements of carbonyl sulfide (OCS) in the 2v3, v1+2v2+v3, and 4v2+v3 bands

To support planetary studies of the Venus atmosphere, we measured line strengths of the 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ bands of the primary isotopologue of carbonyl sulfide (¹⁶O¹²C³²S), whose band centers are located at 4101.387, 3937.427, and 4141.212 cm⁻¹, respectively. For this, infrared absorption spectra in normal carbonyl sulfide (OCS) sample gas were recorded at an unapodized resolution of 0.0033 cm⁻¹ at ambient room temperatures using a Bruker Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory. The FTS instrumental line shape (ILS) function was investigated, which revealed no significant instrumental line broadening or distortions. Various custom-made short cells and a multi-pass White cell were employed to achieve optical densities sufficient to observe the strong 2v₃ and the weaker bands in the region. Gas sample impurities and the isotopic abundances were determined from mass spectrum analysis. Line strengths were retrieved spectrum by spectrum using a non-linear curve fitting algorithm adopting a standard Voigt line profile, from which Herman–Wallis factors were derived for the three bands. The band strengths of 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ of ¹⁶O¹²C³²S (normalized at 100% of isotopologue) are observed to be 6.315(13)×10⁻¹⁹, 1.570(2)×10⁻²⁰, and 7.949(20)×10⁻²¹ cm⁻¹/molecule cm⁻², respectively, at 296 K. These results are compared with earlier measurements and the HITRAN 2004 database.     

Spectral characterization and energy levels of Cr:Sc2(MoO4)3 crystal

This paper reports the spectral properties and energy levels of Cr³⁺:Sc₂(MoO₄)₃ crystal. The crystal field strength Dq, Racah parameter B and C were calculated to be 1408 cm⁻¹, 608 cm⁻¹ and 3054 cm⁻¹, respectively. The absorption cross sections σ_α of ⁴A₂→⁴T₁ and ⁴A₂→⁴T₂ transitions were 3.74×10⁻¹⁹ cm² at 499 nm and 3.21×10⁻¹⁹ cm² at 710 nm, respectively. The emission cross section σ_e was 375×10⁻²⁰ cm² at 880 nm. Cr³⁺:Sc₂(MoO₄)₃ crystal has a broad emission band with a broad FWHM of 176 nm (2179 cm⁻¹). Therefore, Cr³⁺:Sc₂(MoO₄)₃ crystal may be regarded as a potential tunable laser gain medium.     

The ν1 and ν3 Bands of the OOO Isotopomer of Ozone

Using 0.002 cm⁻¹ resolution Fourier transform absorption spectra of an ¹⁷O-enriched ozone sample, an extensive analysis of the ν₃ band together with a partial identification of the ν₁ band of the ¹⁷O¹⁶O¹⁷O isotopomer of ozone has been performed for the first time. As for other C_2v-type ozone isotopomers [J.-M. Flaud and R. Bacis, Spectrochim. Acta, Part A 54, 3–16 (1998)], the (001) rotational levels are involved in a Coriolis-type resonance with the levels of the (100) vibrational state. The experimental rotational levels of the (001) and (100) vibrational states have been satisfactorily reproduced using a Hamiltonian matrix which takes into account the observed rovibrational resonances. In this way precise vibrational energies and rotational and coupling constants were deduced and the following band centers ν₀(ν₃) = 1030.0946 cm⁻¹ and ν₀(ν₁) = 1086.7490 cm⁻¹ were obtained for the ν₃ and ν₁ bands, respectively.     

Interpretation of scanning tunneling microscopy and atomic force microscopy images of 1T-TiS2

The surface of 1T-TiS₂ was examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The STM and AFM images of this compound were interpreted on the basis of the partial electron density ρ(r,E_F) and total electron density ρ(r) of a slab which consists of six (001) 1T-TiS₂ layers. Electronic structure calculations were performed using the ab-initio Hartree–Fock program crystal. It was found that the bright spots in experimental STM images correspond to sulfur atoms at both positive and negative bias voltages. The AFM image showed a periodicity which can be explained by the atomic corrugation at the surface. Structural defects on the surface were also investigated, and their interpretation constitutes experimental proof that only sulfur atoms were detected by scanning probe microscopies.     

High-resolution infrared study of the 2ν3 (A1, E) and ν1 + ν3 (E) bands of NF3

The 2ν₃ overtone (A₁, E) and the ν₁ + ν₃ (E) combination bands of the oblate symmetric top ¹⁴NF₃ were studied by FTIR spectroscopy with a resolution of 2.5 × 10⁻³ cm⁻¹. Nearly 500 lines up to K_max/J_max = 30/43 were observed for the weak A₁ component reaching the v₃ = 2⁰ substate (1803.1302 cm⁻¹), the majority of which corresponded to reinforced K = 3p-type transitions. For the strong E component reaching the v₃ = 2^±2 substate (1810.4239 cm⁻¹), about 3550 transitions were assigned up to K_max/J_max = 65/69, favoring a clear observation of the ℓ(4, −2) and ℓ(4, 4) splittings within the kℓ = −2 and +4 sublevels, respectively. The two v₃ = 2 substates are linked by the ℓ(2, 2)- and ℓ(2, −1)-type interactions, providing severe crossings, respectively, at K′ = 6 and near K′ = 24 on the v₃ = 2⁺² side. A model working in the D-reduction and including all these ℓ-type interactions could reproduce together 3695 nonzero weighted experimental data (NZW) through 33 free parameters with a standard deviation of σ = 0.357 × 10⁻³  cm⁻¹. As for the ν₁ + ν₃ (E) combination band, about 3690 lines were assigned up to K_max/J_max = 45/55. Its v₁ = v₃ = 1 upper state (1931.577 5 cm⁻¹) was treated using the same model recently applied to the v₃ = 1 (E, 907.5413 cm⁻¹) state. It yielded 21 free parameters through 3282 NZW experimental data, adjusted with σ = 0.344 × 10⁻³  cm⁻¹ in the D-reduction. For the two excited states, the small and unobserved ℓ(0, 6) interaction was tested as useless. To confirm the adequacy of the vibrationally isolated models used, some other reductions of the Hamiltonian were tried. For the v₃ = 2 state, the D-, L-, and LD-reductions led to similar σ’s, while the Q one was not successful. For the v₁ = v₃ = 1 state, the D- and Q-reductions gave comparable σ’s, while the QD-reduction was not as good. The corresponding unitary equivalence relations are generally more nicely fulfilled for the v₃ = 2 state than for the v₁ = v₃ = 1 state. The three derivable anharmonicity constants in cm⁻¹ are x₃₃ = −4.1528, g₃₃ = +1.8235 and x₁₃ = −7.9652.     

New ferromagnetic La3Co2TaO9 double perovskite: Structural and magnetic properties

The new double perovskite La₃Co₂TaO₉ has been prepared by a solid-state procedure. The crystal and magnetic structures have been studied from X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) data. Rietveld refinements were performed in the monoclinic space group P2₁/n. The structure consists of an ordered array of alternating B′O₆ and B″O₆ octahedra sharing corners, tilted along the three pseudocubic axes according to the Glazer notation a⁻b⁻c⁺. Rietveld refinements show that at RT the cell parameters are a=5.6005(7) Å, b=5.6931(7) Å, c=7.9429(9) Å and β=89.9539(7)°, and the refined crystallographic formula of this “double perovskite” can be written as La₂(Co)_2d(Co_1/3Ta_2/3)_2cO₆. Magnetization measurements and low-temperature NPD data show that the perovskite is a ferromagnet with T_C=72 K. At high T it follows the Curie–Weiss law with an effective magnetic moment of 3.82μ_B per Co ion which is very close to spin only Co²⁺ (HS).     

Structural, vibrational and dielectric properties of new potassium hydrogen sulfate arsenate: K4(SO4)(HSO4)2(H3AsO4)

A new compound, K₄(SO₄)(HSO₄)₂(H₃AsO₄) was synthesized from water solution of KHSO₄/K₃H(SO₄)₂/H₃AsO₄. This compound crystallizes in the triclinic system with space group P1¯ and cell parameters: a=8.9076(2) Å, b=10.1258(2) Å, c=10.6785(3) Å; α=72.5250(14)°, β=66.3990(13)°, γ=65.5159(13)°, V=792.74(3) Å³, Z=2 and ρ_cal=2.466 g cm⁻³. The refinement of 3760 observed reflections (I>2σ(I)) leads to R₁=0.0394 and wR₂=0.0755. The structure is characterized by SO₄²⁻, HSO₄⁻ and H₃AsO₄ tetrahedra connected by hydrogen bridge to form two types of dimer (H(16)S(3)O₄⁻?S(1)O₄²⁻ and H(12)S(2)O₄⁻?H₃AsO₄). These dimers are interconnected along the [1¯ 1 0] direction by the hydrogen bonds O(3)-H(3)?O(6). They are also linked by the hydrogen bridge assured by the hydrogen atoms H(2), H(3) and H(4) of the H₃AsO₄ group to build the chain S(1)O₄?H₃AsO₄ which are parallel to the “a” direction. The potassium cations are coordinated by eight oxygen atoms with K-O distance ranging from 2.678(2) to 3.354(2) Å.Crystals of K₄(SO₄)(HSO₄)₂(H₃AsO₄) undergo one endothermic peak at 436 K. This transition detected by differential scanning calorimetry (DSC) is also analyzed by dielectric and conductivity measurements using the impedance spectroscopy techniques. The obtained results show that this transition is protonic by nature.     

Electrical properties of perovskite-type La(Cr1−xMnx)O3+δ

Perovskite-type La(Cr_1−xMn_x)O_3+δ (0.0x1.0) was synthesized using a sol–gel process. The crystal structure of La(Cr_1−xMn_x)O_3+δ changes from orthorhombic to rhombohedral at x=0.6. The Mn⁴⁺ ion content increases monotonically in the range 0.2x1.0. The magnetic measurement of La(Cr_1−xMn_x)O_3+δ indicates that a Mn³⁺ ion is a high-spin state with (d)³(dγ)¹. The variation of the average (Cr, Mn)-O distance is explained by ionic radii of the Cr³⁺, the Mn³⁺, the Mn⁴⁺ ions. Since the log σT–1/T curve is linear and the Seebeck coefficient (α) is independent of temperature, it is considered that La(Cr_1−xMn_x)O_3+δ is a p-type semiconductor and exhibits the hopping conductivity.     

NO dissociation and N2 production in the presence of co-adsorbed SO2 and D2 on Pt(3 3 2)

NO dissociation and subsequent N₂ production in the presence of co-adsorbed S¹⁸O₂ and D₂ on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Reduction of NO by D (D₂ is adsorbed dissociatively on Pt surfaces) proceeds to a limited extent, because this reaction is rate-controlled by NO dissociation and the supply of D atoms at the higher surface temperatures at which NO dissociation becomes significant (350 K and higher). NO–D reaction is suppressed in the presence of S¹⁸O₂, depending significantly on the S¹⁸O₂ coverage and the competition between the reactions NO–D and S¹⁸O₂–D. When the supply of D₂ is limited, e.g., 0.1 L in this study, the presence of S¹⁸O₂ suppresses the NO–D reaction. With a sufficient supply of D₂, e.g., 0.4 L and higher, D-atom competing reactions do not play a role any more because the reactions of both NO and S¹⁸O₂ with D proceed only to a very limited extent. As such, generation of O atoms from S¹⁸O₂ dissociation is the main reaction that leads to the suppression in NO dissociation and consequently, N₂ production.It is also concluded that the presence of S¹⁸O₂ does not seriously poison the active sites on the Pt surface, providing that there is a sufficient D supply to remove O atoms from both NO dissociation and S¹⁸O₂ dissociation.     

High-resolution infrared spectra of HCF3 in the ν6 (500 cm) and 2ν6 (1000 cm) regions: rovibrational analysis and accurate determination of the ground state constants C0 and DK

The high-resolution infrared spectrum of HCF₃ was studied in the ν₆ fundamental (near 500 cm⁻¹) and in the 2ν₆ overtones (near 1000 cm⁻¹) regions. The present study reports on the analysis of the hot bands in the ν₆ region, as well as the first observation and assignment of the 2ν₆² perpendicular band. Using ν₆, 2ν₆^±2–ν₆^±1 and 2ν₆² experimental wavenumbers, accurate coefficients C₀ and D_K⁰ of the K-dependent ground-state energy terms were obtained, using the so-called “loop method.” Ground-state energy differences Δ(K,J)=E₀(K,J)−E₀(K−3,J) were obtained for K=3–30. A least-squares fit of 81 such differences gave the following results (in cm⁻¹): C₀=0.1892550(15); D_K⁰=2.779(26) × 10⁻⁷.     

Line Positions and Intensities of the ν1+ ν2+ 3ν3, ν2+ 4ν3, and 3ν1+ 2ν2Bands of Ozone

Using a Fourier transform spectrometer, we have recorded the spectra of ozone in the region of 4600 cm⁻¹, with a resolution of 0.008 cm⁻¹. The strongest absorption in this region is due to the ν₁+ ν₂+ 3ν₃band which is in Coriolis interaction with the ν₂+ 4ν₃band. We have been able to assign more than 1700 transitions for these two bands. To correctly reproduce the calculation of energy levels, it has been necessary to introduce the (320) state which strongly perturbs the (113) and (014) states through Coriolis- and Fermi-type resonances. Seventy transitions of the 3ν₁+ 2ν₂band have also been observed. The final fit on 926 energy levels withJ_max= 50 andK_max= 16 gives RMS = 3.1 × 10⁻³cm⁻¹and provides a satisfactory agreement of calculated and observed upper levels for most of the transitions. The following values for band centers are derived: ν₀(ν₁+ ν₂+ 3ν₃) = 4658.950 cm⁻¹, ν₀(3ν₁+ 2ν₂) = 4643.821 cm⁻¹, and ν₀(ν₂+ 4ν₃) = 4632.888 cm⁻¹. Line intensities have been measured and fitted, leading to the determination of transition moment parameters for the two bands ν₁+ ν₂+ 3ν₃and ν₂+ 4ν₃. Using these parameters we have obtained the following estimations for the integrated band intensities,S_V(ν₁+ ν₂+ 3ν₃) = 8.84 × 10⁻²²,S_V(ν₂+ 4ν₃) = 1.70 × 10⁻²², andS_V(3ν₁+ 2ν₂) = 0.49 × 10⁻²²cm⁻¹/molecule cm⁻²at 296 K, which correspond to a cutoff of 10⁻²⁶cm⁻¹/molecule cm⁻².     

High temperature ferromagnetism of the vacuum-annealed (In1−xFex)2O3 powders

(In_1−xFe_x)₂O₃ (x = 0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In_1−xFe_x)₂O₃ powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In_1−xFe_x)₂O₃ samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe²⁺ and Fe³⁺ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49-1.73 μ_B/Fe and the Curie temperature around 783 K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe²⁺ and Fe³⁺ ions via an electron trapped in a bridging oxygen vacancy.     

Low voltage electron induced cathodoluminescence degradation and surface characterization of Sr3(PO4)2:Tb phosphor

Tb³⁺-doped Sr₃(PO₄)₂ phosphor was prepared by a sol-gel combustion method. A trigonal structure having Sr and O atoms occupying two different lattice sites were obtained. Scanning Auger nanoprobe was used to analyze the morphology of the particles. Photoluminescence (PL) and cathodoluminescence (CL) properties of Sr₃(PO₄)₂:Tb powder phosphors were evaluated and compared. In addition, the CL intensity degradation of Sr₃(PO₄)₂:Tb was evaluated when the powders were irradiated with a beam of electrons in a vacuum chamber maintained at an O₂ pressure of 1 × 10⁻⁶ Torr or a background pressure of 1 × 10⁻⁸ Torr O₂. The surface chemical composition of the degraded powders, analyzed by X-ray photoelectron spectroscopy (XPS), suggests that new compounds (metal oxides) of strontium and phosphorous were formed on the surface. It is most likely that these compounds contributed to the CL intensity degradation of the Sr₃(PO₄)₂:Tb phosphors. The CL properties and possible mechanism by which the new metal oxides were formed on the surface due to a prolonged electron beam irradiation are discussed.     

Investigation of phase transition mechanisms of CsH3(SeO3)2 single crystals by observation of nuclear magnetic resonance

The relaxation times of the ¹H and ¹³³Cs nuclei in CsH₃(SeO₃)₂ crystals were investigated using FT NMR. The ¹³³Cs spectrum does change from seven resonance lines to one resonance line near T_m (=350 K). The presence of only one ¹³³Cs signal is due to the liquid state resulting from the melting of the crystal. The variation in the separation of the ¹³³Cs resonance lines with temperature indicates that the EFG at the Cs sites produced by the (SeO₃)²⁻ groups varies with temperature, which in turn means that the atoms neighboring ¹³³Cs are displaced. And, the T₁ for ¹³³Cs is very long and undergoes significant changes near T_m. The change in the temperature dependence of T₁ at T_m for the ¹³³Cs nuclei coincides with the melting temperature. These results are compared with those obtained for MH₃(SeO₃)₂ (M=Na, K, and Cs) crystals.     

Action of monoatomic cations on the structure and spectra of Mx(1)M1-x(2)UO2(NO3)3 crystals

The action of the monovalent M⁺ cations on the luminescent properties of the mixed M _x ⁽¹⁾ M _1-x ⁽²⁾ UO₂(NO₃)₃ crystals, where M is Na, K, Rb, Cs, or NH₄ , has been investigated. It has been established that the spectral positions of the bands of vibronic transitions depend linearly on the ratio between the concentrations of the M⁽¹⁰⁾ and M⁽²⁾ cations. It is shown that the crystals considered are composed of l[RbUO₂(NO₃)₃]n[CsUO₂(NO₃)₃] clusters, where l/n = x/(1 - x). The spectral regularities revealed are determined by the partial contributions of the M⁽¹⁾ and M⁽²⁾ cations to their combined, polarizing action on the uranyl complex and are explained by the ligand nature of its highest occupied molecular orbital.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 827–830, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

Oxygen nonstoichiometry of Sr(Co,Fe)O3−δ-based perovskites: I. Coulometric titration of SrCo0.85Fe0.10Cr0.05O3−δ by the two-electrode technique

The p(O₂)–T–δ diagram of perovskite-type SrCo_0.85Fe_0.10Cr_0.05O_3−δ was determined by the coulometric titration technique in the temperature range 770–1250 K at oxygen partial pressures from 8 10⁻¹⁰ to 0.5 atm. Stability of the cubic perovskite phase of SrCo_0.85Fe_0.10Cr_0.05O_3−δ, existing down to the oxygen pressures of 10⁻³–10⁻⁵ atm, was found to be slightly higher than that of SrCo_0.80Fe_0.20O_3−δ, probably due to stabilization of oxygen octahedra neighboring Cr⁴⁺ cations. When the oxygen nonstoichiometry of the Cr-containing perovskite decreases from 0.47 to 0.38, the partial molar enthalpy and entropy for overall oxygen incorporation reaction vary in the ranges −165 to −60 kJ mol⁻¹ and 90 to 150 J mol⁻¹ K⁻¹, respectively. Within the stability limits of the single perovskite phase, the p(O₂)–T–δ diagram can be adequately described by equilibrium processes of oxygen incorporation, cobalt disproportionation and interaction of cobalt and iron cations, with the thermodynamic functions independent of defect concentrations. Increasing grain size in SrCo_0.85Fe_0.10Cr_0.05O_3−δ ceramics from submicron size to 100–200 μm has no effect on the oxygen thermodynamics. The two-electrode coulometric titration technique, based on the alternate use of electrodes for oxygen pumping and e.m.f. measurements, is described and verified by studying oxygen nonstoichiometry of La_0.3Sr_0.7CoO_3−δ and PrO_x.