Formation and structure of the potassium graphites

Abstract

The progressive intercalation of graphite by potassium has been studied by x-ray diffraction methods. It has been established that potassium graphites of stages 4, 3, 2 and 1 (with intercalated potassium layers separated by 4, 3, 2 and 1 graphite layers respectively) can be formed successively within a single graphite sample encapsulated with excess potassium. Each stage was prepared in turn by adjusting the temperature difference between the graphite and the potassium in a specially designed double furnace. The graphite layer stacking sequences and repeat distances for stages 2, 3 and 4 are stage 2 AB| BC| CA| A c =26·2 5 Å stage 3 ABA| ACA| A 24·2 0 Å stage 4 ABAB| BCBC| CACA| A 46·3 5 Å Within each intercalate layer the potassium atoms are distributed irregularly over the centres of carbon hexagons in adjacent graphite layers. The fully ordered structure of the stage 1 compound, A α A β A γ A δ A, has been confirmed.