Dependence of the hall coefficient of soft carbons on heattreatment and doping

✍ Scribed by J. Bulawa; S. Mrozowski; A.S. Vagh

• Publisher: Elsevier Science
• Year: 1972
• Tongue: English
• Weight: 969 KB
• Volume: 10
• Category: Article
• ISSN: 0008-6223
• DOI: 10.1016/0008-6223(72)90044-9

✦ Synopsis

A b s t r a c t -I n an effort to study the electronic band structure of pregraphitic carbons, and supplement and crosscheck the information obtained by the ESR technique, the Hall coefficient was measured at room and liquid nitrogen temperature for two soft carbon materials. Samples heattreated from 1500 to 3200°C were investigated by introducing acceptors (boron, bisulphate) and/or donors (sodium, potassium). Using the total change in the Hall coefficient when the Fermi level sweeps across the band overlap as a measure of the degree of overlap, it was found that as one approaches the turbostratic carbons, the small graphite band overlap slightly decreases at first, but after that, starts rapidly increasing as the crystalline disorder increases. No indication of a possible presence of a band gap in pregraphitic carbons is found, but rather a wide mixed up overlap region, with the mobility of holes exceeding the mobility of electrons. It was also found that in soft carbon materials heattreated to below 1840°C, the acceptors invert their behavior by starting to act as donors. The well-known Hall effect minimum at H T T 1650 for the Texas coke is shown to be most probably an impurity effect.