Crystalline orthorhombic Ln[CO3][OH] (Ln=La, Pr, Nd, Sm, Eu, Gd) compounds hydrothermally synthesised with CO2 from air as carbonate source

Abstract

Abstract Crystalline orthorhombic rare earth carbonate hydroxides Ln[CO3][OH] (Ln=La, Pr, Nd, Sm, Eu, Gd) were synthesised as phase pure powders via a simple hydrothermal reaction. CO2 from air acted as natural carbonate source and cetyltrimethylammonium bromide was added as templating agent to an aqueous rare earth nitrate solution. Single-crystal X-ray structure determination was performed on La[CO3][OH] (Pnma, a=7.4106(5), b=5.0502(3), c=8.5901(6) Å, 563 independent reflections, 38 refined parameters, wR2=0.037), Pr[CO3][OH] (Pnma, a=7.2755(4), b=4.9918(3), c=8.5207(5) Å, 744 independent reflections, 38 refined parameters, wR2=0.04), Eu[CO3][OH] (Pnma, a=7.1040(4), b=4.8940(3), c=8.4577(5) Å, 1649 independent reflections, 38 refined parameters, wR2=0.05) and Gd[CO3][OH] (Pnma, a=7.069(7), b=4.874(5), c=8.464(9) Å, 431 independent reflections, 38 refined parameters, wR2=0.051). These findings are supported by powder XRD, infrared spectroscopy, UV/Vis spectroscopy and, for Pr[CO3][OH] and Eu[CO3][OH], by measurements of the non-linear optical properties. Thermal analysis could demonstrate the possible use of the Ln[CO3][OH] phases as precursors for rare earth carbonate dioxides Ln 2[CO3]O2 and rare earth oxides Ln 2O3. The decomposition products inherit the precursor’s morphology. The lattice parameters of Pr2[CO3]O2 were refined from high-temperature powder XRD data.