Crystal Structure and Phase Transitions of Gd(CO3)OH Studied by Synchrotron Powder Diffraction

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

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.

Optimization of the Magnetocaloric Effect in Low Applied Magnetic Fields in LnOHCO3 Frameworks

This study probes the structure and magnetocaloric effect of the LnOHCO₃ (Ln = Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, and Er³⁺) frameworks. The combination of single crystal X-ray and neutron powder diffraction indicates that these materials solely adopt the P2₁2₁2₁ structure under these synthetic conditions and magnetic susceptibility measurements indicate they remain paramagnetic down to 2 K. We show that the magnetocaloric effects of TbOHCO₃ and DyOHCO₃ have peak entropy changes of 30.99 and 33.34 J kg^-1 K^-1 for a 2-0 T field change, respectively, which are higher than that of the promising GdOHCO₃ framework above 4 K in moderate magnetic fields. The magnetic entropy changes of TbOHCO₃ and DyOHCO₃ above 4 K for smaller than 2 T field changes also exceed those of Gd₃Ga₅O₁₂ and Dy₃Ga₅O₁₂, making them suitable magnetic cooling materials for use at liquid helium temperatures using the low applied magnetic fields accessible using permanent magnets, advantageous for efficient practical cooling devices.

Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials

Rare-earth carbonate nano- and micro-materials are reviewed, focusing on factors that influence the morphology and luminescence, as well as their applications as precursors and sacrificial templates for other materials.