Analysis of aluminum tungsten oxide ceramics synthesized by a high-power cw CO2 laser

Abstract

Highpower closedcycle subsonic cw CO laser excited by a transverse selfsustained discharge Appl. Phys. Lett. 46, 537 (1985); 10.1063/1.95584Sintering of new oxide ceramics using a high power cw CO2 laser Ceramics in the Al,Os-WOs system have been produced by laser irradiation. Examination of the products by scanning electron microscopy showed that a cell structure had formed in the specimens. A comparison of the properties of the samples synthesized by laser and by conventional sintering methods showed that the laser technique can produce new materials with some unique properties such as the linear decrease in resistivity of Al,Os-50 mol % WOs specimens with increasing temperature over the range of 10-150 "C. X-ray photographic powder analysis indicated that the conducting phase in the specimen is a nonequilibrium product: AI,WOs tungsten bronze.

Electrical Properties of Laser‐Synthesized Aluminum Oxide‐Tungsten Oxide Ceramics

“…The resistivity initially decreased, because a tungsten impurity was incorporated into the lattice of the Al 2 O 3 during the rapid-quenching process of the material melts, and the impurity content in the Al 2 O 3 lattice increased as the WO 3 content of the initial powder compact increased. 13 At 80 mol% WO 3 , the composition of the samples approached the stoichiometry of Al 2 (WO 4 ) 3 , considering the loss of WO 3 during laser irradiation (Table I in Li et al 6 ). The insulating nature of Al 2 (WO 4 ) 3 had an important role in yielding the product with the higher resistivity ().…”

“…The I-V characteristics of selected samples were examined using an oscilloscope and the circuit described by Li et al 6 The frequency for the ac measurement was 50 Hz.…”

“…L ASER synthesis of ceramics is a new technique, initiated in 1984 by Okutomi et al 1 and used later by other researchers to synthesize ceramics with high toughness, hardness, and melting points from ceramic powders. [2][3][4][5] In 1993, Li et al 6 first used this method to synthesize electronic ceramics. Those researchers obtained new materials from the Al 2 O 3 -WO 3 system that had a unique black and lustrous color and unique semiconductor properties and cell structure; the materials exhibited an endothermic phenomenon at 539°C, which was accompanied by weight loss above that temperature.…”

“…In addition to the above-mentioned properties, the materials have a linearly negative temperature coefficient (NTC) effect; 6 that is, in some composition and temperature ranges, the material resistance can decrease linearly as the temperature increases. In 1976, Matsuoka 7 was the first researcher to successfully obtain a thermistor material with this unique property, from the Sb 2 O 3 -WO 3 -CdO 2 system.…”

“…Laser-synthesized ceramics of the Al 2 O 3 -WO 3 system 6 are nontoxic and have excellent acid resistance (>99.94%) and good alkali resistance (>99.66%) when the WO 3 content is Յ50 mol% in the initial powder compacts. According to the analysis described by Li et al, 6 these ceramics are composed of four phases (see Table I)-i.e., Al 2 O 3 , Al 2 (WO 4 ) 3 , WO 3 , and Al x WO 3 (Al x WO 3 is a nonequilibrium phase that does not exist in the Al 2 O 3 -WO 3 equilibrium phase diagram). Energydispersive X-ray analysis (EDAX) results 13 have proven that a tungsten impurity is incorporated into the Al 2 O 3 lattice during solidification of the material melts.…”