Arsenide

Arsenides. The crystal structure of Nb4As3 has been determined. It consists of a complicated arrangement of Nb As prisms, with one additional Nb in a cubic hole, and one additional As atom situated in another hole between the 

Arsenides.—Some indications of the complexity of binary arsenide structures are apparent from recent X-ray investigations. In the new intermetallic compound Ca2As3, As4 and Asg chains are present in a 1 1 ratio, with As—As distances ranging between 2.47 and 2.58 As units occur in the simple arsenide CaAs, which has an anti-NiAs structure, and here the As—As separation is 2.563 The ternary arsenides CasGa2As6 and Ca4Ga3Ass have also been synthesized, the structure of the former containing layers of Ca—As octahedra and tetrahedra. As expected from valence considerations, As2 units are present 

Crystal structures have been reported for the and y modifications of VsAsa and CrsAsa and for NbaAs. Complete solid solubility has been found in the CrP-CrAs, CrAs-CoAs, and FeAs-CoAs systems, with the phosphorus and arsenic atoms randomly arranged in a MnP-type structure. 

Arsenic and bismuth vapours, at elevated temperatures, produce insertion-type bronze phases on interaction with 

So far two technetium arsenides, TcjAsy and TC2AS3, have been synthesized upon reacting the powdered elements in various ratios at 600-900 C and annealing the samples at 900 to 950 C. 

TC3AS7 is reported to crystallize in the cubic structure with the lattice constant =8.702 A and to be isostructural with RC3AS7, which is diamagnetic and shows non-mctallic behavior. From density measurements the unit cell of Rc3As7 was found to contain four formula units [19]. 

TC2AS3 crystallizes in the triclinic space group PT with the lattice constants =6.574, 6=6.632, c-8.023 A, a=95.69, / =102.03, 7=104.31 , and four formula units per cell. The compound is isostructural with TC2P3, as mentioned before. The structure is closely related to the monoclinic structure of IVI02AS3, from which it can be derived by distortion and by doubling of one translation period [20]. 

Of the binary oxides only TCO2 and TC2O7 could hitherto be identified unambiguously. 

Attempts have been made to synthesize an oxide that is intermediate in composition between Tc and TCO2. Mixtures of Tc and TCO2 were prepared in different ratios, wrapped in platinum foil, vacuum-sealed into Vycor tubes, and heated at about 970 °C for 4.5 days. The distorted rutile structure of TCO2 was noted in all X-ray patterns. In addition, one new phase was found in several samples, which could be indexed on the basis of a primitive pseudocubic unit cell with a=9.45 A. The same new pseudocubic phase was obtained when a mixture of Tc and TCO2 corresponding to the composition TcOo io was heated in a sealed silica tube up to 1250 °C over a 

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M.p. — 116-3 C, b.p. —55°C. An unstable poisonous gas (metal arsenide plus acid or arsenic compounds plus Zn plus dil. acid, AsCla plus LiAlH4) which decomposes to As... 

Figure B3.2.11. Total energy versus lattice constant of gallium arsenide from a VMC calculation including 256 valence electrons [118] the curve is a quadratic fit. The error bars reflect the uncertainties of individual values. The experimental lattice constant is 10.68 au, the QMC result is 10.69 (+ 0.1) an (Figure by Professor W Schattke).

Jin C, Taylor K J, Conoeioao J and Smalley R E 1990 Ultraviolet photoeleotron speotra of gallium arsenide olusters Chem. Phys. Lett. 175 17... 

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

Kher S S and Wells R L 1996 Synthesis and characterization of colloidal nanoorystals of capped gallium arsenide Nanostruct. Mater. 7 591... 

C2.18.4.1 HOMOEPITAXY OF GALLIUM ARSENIDE BY ATOMIC LAYER EPITAXY... 

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