We determined the structures of amorphous diboron trioxide and sodium pentaborate hydrate by X-ray diffractometry. Radial distribution functions (RDF) of those samples were obtained from precisely diffraction data processing. Their short-range ordered structures were determined by model design and quantitative calculations. In amorphous diboron trioxide hydrate, 75% of boron atoms construct planar six-membered boroxol ring and the interatomic distance and the interactions numbers of intra-ring ortho-B—O, meta-O—O, meta-B—B and para-B—O were listed out, where boron-oxygen branched-chain intersects with the plane at a terminal-oxygen with a intersect angle of 125°±15°. The basic structure unit of non-crystalline sodium pentaborate hydrate is formed by two planar six-membered boroxol rings deformed, composed of two boron-oxygen triangles (B_△) and a boron-oxygen tetrahedron (B_□), through the shared B_□. The highly ordered intra-anion interactions are the upmost interactions. Six coordinated Na^＋ connects with the terminal-oxygen of pentaborate to form a contact ion pair with a characteristic distance (B—Na) of 0.330 nm.

Key words: amorphous, X-ray diffraction, diboron trioxide hydrate, sodium pentaborate hydrate, short-range ordered structure, radial distribution function (RDF)