A series of oxygen-contained tungsten films were grown on Si(100) substrates without intentional heating by ultra-high-vacuum reactive magnetron sputtering at a constant argon pressure (P-Ar) of 1.33 x 10(-1) Pa mixed with a wide range of 0, partial pressures (PO) from 1.33 x 10(-4) to 4 x 10(-1) Pa, equivalent to P-O-to-P-A, ratios (P-O/Ar) from 1 x 10(-3) to 3. The effect of varying P-O/Ar on phase evolution was evaluated by annealing the films in a controlled atmosphere (argon or oxygen) at 500 or 700 degrees C for 1 h. Grazing incident X-ray diffraction and transmission electron microscopy, together with the data of electrical resistivity and deposition rate, reveal that gradually increasing C, P-O/Ar induces a sequence of phase transitions from nanocrystalline beta-W(O) (P-O/Ar<= 0.1), amorphous WO2 (P-O/Ar=0.6) to amorphous WO3 (P-O/Ar>= 2). When annealed in argon atmosphere, the amorphous WO, and WO3 exhibit a very different magnitude of crystallization temperature (T-c) and can be transformed, respectively, into monoclinic WO2 (T-c=500 degrees C) and tetragonal WO3 (T-c=700 degrees C). However, the oxidizing atmosphere plays a role to accelerate significantly the crystallization of the amorphous WO, into a completely different phase (monoclinic WO3) at a significantly reduced Tc of 500 'C. (c) 2005 Elsevier B.V. All rights reserved.