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Single crystals of the methylammonium (MA) lead halides MAPbI 3 , MAPbBr 3 , and MAPbCl 3 have been investigated using infrared spectroscopy with the aim of analyzing structural and dynamical aspects of processes that enable the ordering of the MA molecule in the orthorhombic crystal structure of these hybrid perovskites. Our temperature-dependent studies were focused on 2 the analysis of the CH/NH rocking, C-N stretching, and CH/NH bending modes of the MA molecule in the 800-1750 cm -1 frequency range. They deliver a direct comparison of the behavior of the three halides on crossing the orthorhombic-tetragonal phase transition in MA lead halide single crystals. Drastic changes of all vibrational modes close to the phase transition were clearly observed. Additional spectral features that were not discussed previously are pointed out. The transformation of the 2-dimensional orthorhombic hydrogen bond layers into a more 3-dimensional arrangement in the tetragonal phase seems to be an important feature providing deeper insight into the mechanisms that lead to a free-rotating MA molecule in the inorganic host structure. The change of the molecules site symmetry in the tetragonal crystal structure seems to be an important feature of the orthorhombic-tetragonal phase transition. For low temperatures it can be stated that the iodide is stronger influenced by hydrogen bonding than the bromide and the chloride. FIGURE 1 Visualization of MAPbI 3 tetragonal (a, b), MAPbI 3 orthorhombic (c, d) andMAPbBr 3 orthorhombic (e, f) crystal structure. Two hydrogen bond layers, layer A and layer B, can be identified. Layer A is shown in b), d) and f). The only difference between layer A and layer B is the orientation of the MA molecule axis. All N-H...I bond lengths are the same for both layers A and B (Table S5). Hydrogen atoms are not shown in the tetragonal structure. The colors refer to the following elements: purple -iodine, dark blue -bromide, dark grey -lead, brown -carbon, light blue -nitrogen, light orange -hydrogen. 8 X-ray diffractionSample purity was proven by X-ray powder diffraction analysis. The measurement was performed by a Panalytical X'Pert Pro MRD powder diffractometer with sample spinner (Bragg-Brentano geometry, λ = 1.5406 Å Cu Kα with 40kV/30mA, step size 0.0032 and time per step 597.72 sec, 2θ from 11-81°). The analysis was done with HighScore Plus Version 3.05. No impurities were observed. FTIR microscope spectrometryInfrared spectra were recorded on a Bruker Vertex 80v FTIR spectrometer, equipped with a globar light source, a KBr beam-splitter and a Bruker Hyperion 2000 microscope using Cassegrainian objectives and an MCT Hg-Cd-Te detector. A detector nonlinear correction routine was applied using the OPUS software package (Bruker). A Linkam THMS600 stage was used for cooling under Argon atmosphere. The thermocouple was calibrated using melting points of different salts (melting points between 580 K and 1074 K) as described elsewhere. 50 The 0°C point (freezing of H 2 O) was included in the calibration line....

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Concentrations of a series of trace elements of 14 quartz samples from various geological settings (hydrothermal, igneous, metamorphic) in Norway were determined by LA-ICP-MS. FTIR spectroscopy was applied to the same quartz crystals in order to determine the H concentrations and the speciation of H in the quartz lattice. A refined hypothetical charge neutrality equation is suggested, where the atomic ratio of (Al3+ + Fe3+ + B3+) to (P5+ + H+ + Li+ + Na+ + K+) should correspond to 1 for natural quartz crystals. The determined concentrations of Al, Fe, B, P, Li, K and OH- species confirm approximately the charge neutrality equation. The high H/(Li+K+P) ion ratio of igneous quartz compared to hydrothermal and metamorphic quartz, suggests that igneous quartz preferentially incorporates H as OH- in lieu of Li, K and P. The results confirm that the FTIR absorption of the OH- band at 3595 cm-1 is attributed to structural B defects in the quartz lattice. The dominating H impurity in most of the quartz samples is, however, molecular H2O. The molecular H2O is presumably related to waterbearing micro pores and not to visible fluid inclusions, because the spectra were recorded from microscopically clear crystals.