Structural and conductivity studies in LiFeP2O7, LiScP2O7, and NaScP2O7

Structural studies of LiScP₂O₇ by Rietveld refinement confirm that this material is isostructural with LiFeP₂O₇ studied previously. However, NaScP₂O₇ shows a structure different from the structural types of the basic group of Na^IM^IIIP₂O₇ known thus far. Systematic ranges for the six structural types of A^IM^IIIP₂O₇ are presented in terms of ion radii sums and ratios. The framework of LiMP₂O₇ (M=Sc, Fe) has rather wide tunnels running along the crystallographic c-axis. This feature has determined our interest to check the ion conductivity in A^IM^IIIP₂O₇ (A=Li, Na; M=Sc, Fe). The bulk conductivity, however, is low in these compounds, 10⁻⁶–10⁻⁷ S/cm at 300 °C, as determined by impedance spectroscopy. In order to facilitate the conductivity via normal lithium sites, heterovalent substitution is used. Received: 30 April 1999 / Accepted: 15 June 1999     

Low-lying excited states and photodissociation studies of cis-BrONO

A computational study of the low-lying singlet and triplet states of bromine nitrite, cis-BrONO, is presented. Calculations of excitation energies and oscillator strengths are reported using multi-reference configuration interaction, MRD-CI, methods in conjunction with the cc-pVDZ?+?sp and cc-pVTZ?+?sp basis sets. In agreement with recent experimental work the calculations find two important transitions, namely to the states 2¹ A′ at 3.99?eV and 4¹ A′ at 5.27?eV. The corresponding measurements obtained 3.87 and 5.44?eV, respectively. Both states show multi-reference character, representing a linear combination of 3a″?→?4a″ and 9a′?→?10a′ transitions. The potential energy curves for the Br+ONO dissociation are repulsive for both states indicating possible photodissociation. BrO+NO products are not favoured because the corresponding potential energy curves show barriers on the order of 0.5?eV.     

XRD,impedance, and Mössbauer spectroscopy study of the Li<Subscript>3</Subscript>Fe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> + Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> composite for Li ion batteries

The synthesis procedure of the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite is presented. The monoclinic (A type) and hematite phases were detected by X-ray diffraction after the synthesis of the composite. The structural α–β (at a temperature of 460 K) and β–γ (at a temperature of 523 K) phase transitions in the composite were indicated by the anomalies of the electrical conductivity, dielectric permittivity, and changes of activation energies of conductivity. Two phase transitions have been detected in the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite by ⁵⁷Fe Mössbauer spectroscopy: the phase transition in Li₃Fe₂(PO₄)₃ from the paramagnetic to antiferromagnetic phase at temperature T _N?=?29.5 K and the Morin phase transition in Fe₂O₃ at temperature T _M?=?235 K.