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Thesis (Ph. D.)--Johns Hopkins University, 1917. / Biographical.

Thesis (Ph. D.)--Johns Hopkins University. / Biographical.

A study has been made of the system BaO - A1203 - H20 under varying conditions (temperature, pressure and time) using different starting materials. Of the nine previously reported barium a luminate hydrates, eight (B 1.1AH,* α-BAH2, α-BAH 4' β-BAH4, B1.1AH6, BAH7 , B2AH5 and B3AH7) have been confirmed, and one (Thilo's β-BAH2) was not confirmed. In addition, eight new binary or ternary compounds have been obtained, viz: Y-BAH 2, BAHO.5, B2AH2, B2AH, B3AH6, β-B3A, BxAγHz and BxA. The formula of the last two compounds are uncertain. Besides these, the existence of B2A, which has been questioned by many investigators, has been confirmed. Lattice constants and other crystallographic data have been determined for most of the above compounds, mainly by single crystal X-ray methods or in two cases by selected area electron diffraction. The compounds have also been studied in the following ways: (1) X-ray powder diffraction, (2) infrared spectroscopy, (3) differential thermal analysis, (4) thermogravimetric analysis, (5) static thermal analysis, (6) optical microscopy, (7) chemical analysis and (8) determination of density. The results of these studies are reported. The detailed structure analyses of B3AH6, B2AH5 and α-BAH2 have been performed by X-ray methods. The results show that B3AH6 has the hydrogarnet structure, B2AH5 contains isolated polynuclear anions of formula A12(OH)4-10 formed by sharing edges of centrosymmetrically related Al(OH)6 octahedra, and α-BAH2 is built from isolated helical chains formed from A104 tetrahedra. (*Cement chemical abbreviations: B = BaO, A = Al203, H = H20).

The absorption of polarized infrared radiation by single crystals of barium formate has been recorded between 4000 and 500 cm⁻¹. Factor group splitting has been observed for molecular modes and for some of the overtones and combinations. Lattice mode frequencies are inferred from combinations with molecular modes. The infrared spectrum of polycrystalline lead and sodium formate, and of aqueous barium formate has been similarly recorded and compared with that of crystalline barium formate. The nuclear magnetic resonance spectrum of barium formate has been recorded, and a discrepancy between the theoretical and experimental second moment indicates that a previously proposed crystal structure is incorrect. However, an X-ray and infrared study of a single crystal confirm that the factor group of barium formate is P2₁2₁2₁ and that there is no degradation of the crystal symmetry due to a possible distortion of the C-H bond of the formate ion. It is concluded that the coordinates of the carbon and oxygen atoms are incorrect in the original crystal structure determination. The nuclear magnetic resonance spectrum of lead formate also indicates that the crystal structure of this compound is in error, but no attempt is made to elucidate the correct structure. / Science, Faculty of / Chemistry, Department of / Graduate

Novel low temperature wet chemical processes for the synthesis of gels and ultrafine powders of BaTiO₃ and BaTi₄O₉ were developed. Under acidic conditions a titanyl acylate precursor was obtained by molecular modification of titanium isopropoxide. In the sol-gel process, amorphous BaTiO₃ gels obtained under acidic conditions were heat treated at ≈950-1000°C yielding fine (≈ 1-3 μm), high purity (99.9%) stoichiometric (Ba/Ti = 0.99) BaTiO₃ powders. In the sol-precipitation process, ultrafine (≈ 10 nm) crystalline BaTiO₃ powders were directly precipitated at low temperatures (<100°C) from a stoichiometric titanium acylate- barium acetate sol (pH > 13.5). Precursor powders obtained by hydrolytic decomposition of barium and titanium alkoxides were heat treated at 1100°C to obtain high purity, homogeneous, single phase BaTi₄O₉ powders. Atomistic pathways for the evolution of crystalline phases from amorphous gels and powders were investigated. The microstructure and electrical properties of sintered BaO-TiO₂ ceramics were studied and correlated with the powder processing conditions. The structures of crystalline and amorphous forms of some materials in the BaO-TiO₂ system were simulated using molecular dynamics computer techniques to develop a fundamental understanding of structure-property relationships for BaTiO₃ and TiO₂ containing glasses.

Ultracold molecules promise a revolutionary test bed for quantum science with applications ranging from experiments that probe the nature of our universe, to hosting new platforms for quantum computing. Cooling and trapping molecules in the ultracold regime is the first step to unlocking the wide array of proposed applications, and developing these techniques to control molecules is a key but challenging research field. In this thesis, we describe progress towards a new apparatus designed to cool and trap barium monohydride (BaH), a molecule that is amenable to laser cooling and has prospects as a precursor for ultracold atomic hydrogen. The same complexity that makes molecules interesting objects of study creates challenges for optical control. To mitigate some of these challenges, we first cool the molecules using cryogenic techniques and technologies. Our apparatus uses a cryogenic buffer gas to thermalize BaH within a contained cell. The molecules are extracted into a beam with millikelvin transverse temperature, and forward velocities <100 m/s. The BaH beam in this work is the brightest hydride beam to date, with molecule density and kinetic characteristics well suited for laser cooling and trapping.