Crystal Growth of Sodium Iron Titanium Bronze Compounds under Hydrothermal Conditions

Abstract

Single crystals of four types of oxides consisting of sodium iron and titanium were grown hydrothermally under reduced conditions starting with a mixture of TiO₂ (rutile) and metallic Fe powder in the ratio 5:1 (weight basis) at 650°C and 1000kg/cm² in 10m NaOH solution for different durations. Formation of single crystals having an orthorhombic cell was observed after one week. In longer runs under the same conditions the initial phase undergoes transformation to form crystals having hexagonal and orthorhombic cells and finally to monoclinic freaudenbergite (Na₂O·Fe₂O₃·7TiO₂). From Mössbauer and EPMA data, the common chemical formula for these new phases can be written as (Na_xFe ²⁺_y ) · [Ti_pFe ²⁺_q Fe ³⁺_r O_2-δ)]_n.