[en] Full text The L-histidine hydrobromide monohydrate (C₆H₁₂N₃O₃Br) are promissing material for optical second harmonic generation [1]. Single crystals of L-histidine hydrobromide monohydrate (LHB) have been growth by slow evaporation solution growth technique.In this work we have studied the stability of LHB crystal as function of temperature using three techniques: X-ray diffraction (XRD) in association with Rietveld refinement, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The TGA, DTA and DSC measurements were carried out between 293 and 773 K in the nitrogen atmosphere. The heating rate was maintained at 10 deg C/min. In order to analyze the X-ray diffractogram of the crystals varying temperature measurements were performed in a powder diffractometer with Cu, Kα radiation (l = 1.5418 Å) operating at 40 kV/30 mA with an Anton-Paar TTK450 temperature chamber attached. The samples were heated at 298 up to 463 K and the patterns were obtained at a 0.02 deg (2θ) step size and 3 s/step in the 10-45 deg (2θ) range. From the combination of these techniques, we are able to study the phase transition of the crystal which occurs around the temperature of 383 K. The lattice parameters of a new phase were determinated from powder diffraction by the Le Bail method [2] carried out with the GSAS refinement program. XRD analysis has revealed that the compound crystallizes in the orthorhombic system with space group P212121 . The unit cell parameters obtained at room temperature are: a=7.05339(6) Å, b=9.04180(3) Å, c=15.27377(1) Å. Reference: [1] ITTYACHAN, R. et al. Growth and characterization of semiorganic non-linear optical LHB single crystal. Materials Chemistry and Physics, 93, 2005. 275-276. [2] LE BAIL, A.; DUROY, H.; FOURQUERT, J. L. Ab-initio structure determination of LiSbWO6 by X-ray powder diffraction. Materials Research Bulletin, 23, 1988. 447-452. (author)