Nb2o5

Li₃NbO₄ was prepared by solid-state reaction from stoichiometric amounts of Li₂CO₃ (> 98.5%; Kanto Kagaku) and Nb₂O₅ (99.9%; Wako Pure Chemical Industries) at 950 °C for 24 h in air. Li_1.3Nb_0.3Me_0.4O₂ (Me=Fe³⁺, Mn³⁺ and V³⁺) samples were prepared from Li₂CO₃, Nb₂O₅ and precursors containing each transition metal: Mn₂O₃, Fe₂O₃ (99.9%; Wako Pure Chemical Industries), V₂O₃ (98%; Sigma-Aldrich Japan). Mn₂O₃ was obtained by heating of MnCO₃ (Kishida Chemical) at 700 °C for 12 h. The precursors were thoroughly mixed by wet mechanical ball milling and then dried in air. Thus obtained mixtures of the samples were pressed into pellets. The pellets were heated at 900 °C for 12 h in air (Fe³⁺) or inert atmosphere (Mn³⁺ and V³⁺). The samples were stored in an Ar-filled glove box until use.
Li_1.2Ti_0.4Mn_0.4O₂ was prepared from Li₂CO₃, TiO₂ (Anatase, 98.5%; Wako Pure Chemical Industries), and Mn₂O₃. The precursors were thoroughly mixed by wet mechanical ball milling and the mixture was heated at 900 °C for 12 h in inert atmosphere. Particle morphology of the samples was observed using a scanning electron microscope (JCM-6000, JEOL) with acceleration voltage of 15 keV.

The target materials, generally
with composition xLi₃NbO₄–(1
– x)NiO, were synthesized by the solid-state
method. Li₂CO₃ (98.5%, Kanto Kagaku), NiCO₃·Ni(OH)₂·4H₂O (Kishida Chemical),
and Nb₂O₅ (99.9%; Wako Pure Chemical Industries)
were mixed, followed by wet ball-milling with methanol at 300 rpm
for 6 h. After drying, the obtained powder was pressed into pellets
under a pressure of 20 MPa. The obtained pellets were calcined in
air at 1000 °C for 48 or 2 h.
A polycrystalline sample
of SrFeO₃ was synthesized via a solid-state reaction under
high-pressure conditions. A mixture of stoichiometric amounts of SrCO₃ and Fe₂O₃ was first calcined at 1200
°C for 24 h in air. The obtained calcined powder was sealed in
a Pt capsule with an oxidizing agent, KClO₄, and held at
4.0 GPa and 1000 °C for 30 m before being quenched to room temperature.
The pressure was then reduced slowly to ambient. The reacted sample
was washed with distilled water to remove the residual KCl and KClO₄.

0.1 g of graphite (8.33 × 10⁻³ mol, KANTO CHEMICAL Co., Inc.) or MPC (8.33 × 10⁻³ mol, TOYO TANSO Co., Ltd), 0.1 g of Nb₂O₅ (3.76 × 10⁻⁴ mol, FUJIFILM Wako Pure Chemical Co., Ltd), and 0.035 g of K₂CO₃ (2.53 × 10⁻⁴ mol, FUJIFILM Wako Pure Chemical Co., Ltd) were mixed by mortar and obtained mixture was added on the platinum boat. The reactants on the platinum boat were placed in the oven and calcined at different temperature (800–1150 °C) for 10 h under N₂ atmosphere. After cooling to room temperature, NbC was obtained. On the investigation of reaction mechanism, KNbO₃ (KOJUNDO CHEMICAL LABORATORY Co., Ltd) was also used as reactants.