Über die Bildungsbedingungen und Eigenschaften des β‐Wolframs. Weiterer Beitrag zur Reduktion des Wolframtrioxyds

Abstract

Es wurde bewiesen, daß β‐W weder ein metallisches Oxyd, noch ein Hydrid, sondern ein Metall ist. Nachdem die Bedingungen, unter denen röntgenreines β‐W gewonnen werden kann, ermittelt worden sind, wurde ein Verfahren angegeben, mit dessen Hilfe das β‐W in Chargen von 5–10 g dargestellt werden kann. Die chemischen und physikalischen Eigenschaften, die Kristallstruktur, Oxydation und Dichte des β‐Wolframs, fernerhin die β‐α‐Modifikationsumwandlung und das damit verbundene Kristallwachstum wird eingehender behandelt. Schließlich wird der Reaktionsmechanismus der WO3‐Reduktion mittels H2 qualitativ aufgeklärt und zusammenfassend mit einem schematischen Bild der möglichen Reaktionen, sowie mit einem kinetischen Phasendiagramm erhellt.

Low-resistivity α-phase tungsten films grown by hot-wire assisted atomic layer deposition in high-aspect-ratio structures

“…Tungsten is known to exist in α, β and γ crystal phases [34,35]. Among them, α is the most stable phase; β-phase is metastable and is normally formed by W 3 W or W 3 O clusters [36,37]. Moreover, β-phase can be transformed into α-phase by annealing above 600°C [38,39].…”

“…α-W possesses a body centered cubic lattice with a lattice constant of 0.316 nm [40], whereas β-phase has a cubic A 3 B (A 15) crystal structure with a lattice constant of 0.504 nm [41]. Bulk β-phase W is known to possess a higher resistivity, normally above 100 and up to 1290 μΩ•cm [36,37,42], compared to 5.6 μΩ•cm of bulk α-phase W [1].…”

Comparison of tungsten films grown by CVD and hot-wire assisted atomic layer deposition in a cold-wall reactor

“…31,33 a-W is the most stable phase; it has a body centered cubic lattice with a lattice constant of 0.316 nm. 34 The b-phase exhibits a cubic A 3 B (A 15) crystal structure and is formed by W 3 W or W 3 O clusters 35,36 with a lattice constant between 0.503 and 0.504 nm. 37 It is reported that the b-phase is metastable and can be transformed into the a-phase upon annealing at 650-750 C. 38,39 In addition, the c-phase has only been found at the beginning of sputtering and readily forms a-W. 23 For applications in semiconductor devices, a-W is more desired attributed to its low resistivity; while b-W is adopted in transition edge sensors due to its superconducting properties where transition temperatures is as high as 4 K. 37,40 Figure 8 demonstrates the XRD patterns of W films deposited by the three mentioned methods.…”

Superconductivity in Films ofβTungsten and Other Transition Metals

“…Subsequent workers have found that tungsten can be prepared in the A15 structure with considerably less than this stoichiometric amount of oxygen. 6 In the present investigation, films of a series of transition-metal elements have been studied. Thicknesses of about 1000 A are normally deposited on glass or sapphire substrates by electron-bombardment evaporation.…”