Ladislav Bohaty

Temperature-dependent X-ray and neutron diffraction study of BiB3O6

The structure of bismuth triborate has been analyzed by the combination of neutron and X-ray diffraction on powder and on single-crystalline samples. Bismuth triborate exhibits a distinct anisotropic thermal expansion with the coefficient along a being negative over the wide temperature range studied, 20 to 800 K. The remarkable crystal structure of bismuth triborate with a netlike linkage of rigid borate units [BO3] and [BO4], is found to generate the uncommon thermal expansion behavior. Our investigations gave no evidence for a structural phase transition in bismuth triborate between 3.5 and 999 K at ambient pressure.

On racemic and L-malates: a comparison of their crystal structures

Abstract The crystal structures of eight different L-malates have been determined and refined from single-crystal X-ray diffraction data. The compounds are the monoclinic (space group P21, Z = 2) L-malates Ca(C4H4O5)·3H2O (a = 6.652(1) Å, b = 8.378(1) Å, c = 8.268(1) Å, β = 112.65(2)°, R = 0.027), Ni(C4H4O5)·3H2O (a = 5.762(1) Å, b = 9.006(2) Å, c = 8.406(1) Å, β = 105.54(1)°, R = 0.024), CuH2(C4H4O5)2 (a = 9.911(1) Å, b = 5.271(1) Å, c = 11.510(1) Å, β = 109.33(1)°, R = 0.031), CsH(C4H4O5)·H2O (a = 7.439(1) Å, b = 7.481(1) Å, c = 7.852(1) Å, β = 116.67(1)°, R = 0.027) as well as the four isomorphic tetragonal (space group P41212, Z = 4) L-malates MgH2(C4H4O5)2·4H2O (a = 7.524(1) Å, c = 27.459(2) Å, R = 0.041), MnH2(C4H4O5)2·4H2O (a = 7.548(1) Å, c = 27.707(2) Å, R = 0.027), CoH2(C4H4O5)2·4H2O (a = 7.519(1) Å, c = 27.537(2) Å, R = 0.030) and ZnH2(C4H4O5)2·4H2O (a = 7.533(1) Å, c = 27.360(2) Å, R = 0.029). A comparison of the atomic arrangements of L-malates with their racemic counterparts shows different aspects of symmetry as well as differences in the connectivity of the building units. In addition, for all the compounds, powder diffraction data were collected, analysed and submitted to the powder diffraction file (PDF).

Whispering gallery resonator from lithium tetraborate for nonlinear optics

For second-order nonlinear-optical processes in the ultraviolet, appropriate materials with a sufficiently large band-gap typically exhibit smaller nonlinear coefficients than materials with comparably smaller band-gap. Whispering gallery resonators, with their outstanding quality factors, provide field enhancement and can compensate for these small coefficients. We report on the successful fabrication of a whispering gallery resonator made of lithium tetraborate, a suitable material for ultraviolet applications with a small nonlinear coefficient of d31 = 0:073 pm/V. Quality factors of the order of 108 are observed from the ultraviolet to the near-infrared spectrum. The inferred absorption coefficients of lithium tetraborate are below 0.2 m-1 in the visible and near-infrared. Continuous-wave second harmonic generation from 490 nm light to 245 nm is observed with conversion efficiencies up to 2.2 %.