Crystals of the Mn Ba(BO)F phase were grown from a high-temperature solution. This new fluoride borate is built of positively charged [Ba(BO)] blocks, the so-called "anti-zeolite" pattern. Using X-ray single-crystal diffraction, the bulk atomic arrangement in the centrosymmetric tetragonal unit cell in I4/ mcm could be elucidated. Crystals of the (MnF) group-containing solid solution Mn Ba(BO)F are dark brown in color in contrast to the differently colored crystals of (LiF) group-containing "anti-zeolite" LiBa(BO)F ( P4 bc). According to the electron spin resonance and optical spectroscopic investigation, the absorption spectrum of LiBa(BO)F crystals results from the absorption of light by both exciton and free charge carriers and can be tuned by varying the initial composition of the high-temperature solution.

The first systematic study of the BaO-B 2 O 3 system and barium orthoborate Ba 3 B 2 O 6 (3BaOÁB 2 O 3 ) was reported in 1949. Thereafter, the system was repeatedly refined but the structure of Ba 3 B 2 O 6 compound has not been adequately studied yet. In our study we have, for the first time, obtained the crystalline samples of Ba 3 B 2 O 6 . The solved structure (Pbam, a = 13.5923(4) A, b = 13.6702 The studies of BaO-B 2 O 3 system are complicated by the high reactivity and hygroscopicity of melts. High viscosity of the melts and their tendency for undercooling, glass formation and appearance of metastable equilibriums present a particular problem.Barium oxide BaO melts at 1923°C. The compound crystallizes in a cubic crystal system with the rock salt structure. Boric oxide B 2 O 3 is extremely hydroscopic and is very difficult to crystallize, its melting temperature is 450°C. The structures of two polymorphous modifications of boric oxideÀB 2 O 3 (I) (P3 1 21) 4 and B 2 O 3 (II) (Ccm2 1 ) 5 Àwere studied with adequate accuracy.For the first time, the BaO-B 2 O 3 system was systematically studied by Levin & McMurdie (1949) 6 with the use of annealing and quenching procedures, X-ray powder diffraction and thermal analysis. The middle part of the phase diagram was repeatedly studied by H€ ubner (1969). 8 In addition to the above-listed compounds, three new compounds were established: 2BaOÁ5B 2 O 3 , "2BaOÁB 2 O 3 " and 4BaOÁB 2 O 3 . It should be emphasized that the right stoichiometry assigned to "2BaOÁB 2 O 3 " is 2.5BaOÁB 2 O 3 , which was convincingly shown in.

The α- and β-modifications of barium metaborate are important functional materials used in optoelectronic devices. A new theoretically predicted modification of BaB2O4 has been synthesized under conditions of 3 GPa and 900 °C, using the DIA-type apparatus. The new high-pressure modification, γ-BaB2O4, crystallizes in a centrosymmetrical group of monoclinic syngony (P21/n (#14), a = 4.6392(4) Å, b = 10.2532(14) Å, c = 7.066(1) Å, β = 91.363(10)°, Z = 4). A distinctive feature of the γ-BaB2O4 structure is the presence of edge-sharing tetrahedra [B2O6] which form infinite double chains ∞[B4O4O8/2] stretching along the a axis. The number of known structural types with the [B2O6] group is limited. Phase γ-BaB2O4 has the shortest distance between boron atoms of shared tetrahedra among all currently known compounds. The [B2O6] group angles are 95.5° and 105.5°. Thermodynamic stability and electronic properties of the γ-BaB2O4 modification were studied. The width of the band gap, calculated using the HSE06 functional, is 7.045 eV which implies transparency in the deep-UV region. Experimental and numerical methods which demonstrate a good match were used to the study the Raman spectra of γ-BaB2O4 and β-BaB2O4 modifications. In the Raman spectra of γ-BaB2O4, the most intense band at a frequency of 853 cm–1 was found to correspond to the symmetric bending mode of the B–O–B–O ring in edge-sharing tetrahedra.

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