Creatine: Polymorphs Predicted and Found

Hydrate and anhydrate crystal structure prediction (CSP) of creatine (CTN), a heavily used, poorly water-soluble, zwitterionic compound, has enabled the finding and characterization of its anhydrate polymorphs, including the thermodynamic room temperature form. Crystal structures of the novel forms were determined by combining laboratory powder X-ray diffraction data and ab initio generated structures. The computational method not only revealed all experimental forms but also predicted the correct stability order, which was experimentally confirmed by measurements of the heat of hydration

Creatine: Polymorphs Predicted and Found

Hydrate and anhydrate crystal structure prediction (CSP) of creatine (CTN), a heavily used, poorly water-soluble, zwitterionic compound, has enabled the finding and characterization of its anhydrate polymorphs, including the thermodynamic room temperature form. Crystal structures of the novel forms were determined by combining laboratory powder X-ray diffraction data and ab initio generated structures. The computational method not only revealed all experimental forms but also predicted the correct stability order, which was experimentally confirmed by measurements of the heat of hydration

Mechanical Properties, Quantum Mechanical Calculations, and Crystallographic/Spectroscopic Characterization of GaNbO₄, Ga(Ta,Nb)O₄, and GaTaO₄

Single crystals as well as polycrystalline samples of GaNbO₄, Ga­(Ta,Nb)­O₄, and GaTaO₄ were grown from the melt and by solid-state reactions, respectively, at various temperatures between 1698 and 1983 K. The chemical composition of the crystals was confirmed by wavelength-dispersive electron microprobe analysis, and the crystal structures were determined by single-crystal X-ray diffraction. In addition, a high-P–T synthesis of GaNbO₄ was performed at a pressure of 2 GPa and a temperature of 1273 K. Raman spectroscopy of all compounds as well as Rietveld refinement analysis of the powder X-ray diffraction pattern of GaNbO₄ were carried out to complement the structural investigations. Density functional theory (DFT) calculations enabled the assignment of the Raman bands to specific vibrational modes within the structure of GaNbO₄. To determine the hardness (<i>H</i>) and elastic moduli (<i>E</i>) of the compounds, nanoindentation experiments have been performed with a Berkovich diamond indenter tip. Analyses of the load–displacement curves resulted in a high hardness of <i>H</i> = 11.9 ± 0.6 GPa and a reduced elastic modulus of <i>E</i>_r = 202 ± 9 GPa for GaTaO₄. GaNbO₄ showed a lower hardness of <i>H</i> = 9.6 ± 0.5 GPa and a reduced elastic modulus of <i>E</i>_r = 168 ± 5 GPa. Spectroscopic ellipsometry of the polished GaTa_0.5Nb_0.5O₄ ceramic sample was employed for the determination of the optical constants <i>n</i> and <i>k</i>. GaTa_0.5Nb_0.5O₄ exhibits a high average refractive index of <i>n</i>_D = 2.20, at λ = 589 nm. Furthermore, <i>in situ</i> high-temperature powder X-ray diffraction experiments enabled the study of the thermal expansion tensors of GaTaO₄ and GaNbO₄, as well as the ability to relate them with structural features