ELSEVIER MATERIALS SCIEIICE & EWClWEERlWG A Materials Science and Engineering A217/218 (1996) 198-202 Can we synthesise a dense bundle of quasi one-dimensional metallic wires? Peter P. Edwardsa,*, Paul A. Andersona, Lee J. Woodalla, Adrian Porchb, A. Robert Armstrong” “School OJ Chemistry, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK bSchool of Elertronie aizd Electrical Engineering, The University of Birmingham, Eclgbaston, Birmingham B15 2TT, UK ‘School of Chemistry, The University of St. Andrelw, Fife KYi6 SST, UK Abstract In two timely publications, Kelly [1,2] has recently highlighted the poor prospects for practical quasi one-dimensional electronic devices in the context of existing fabrication technologies. One of the proposed radical alternatives, viewed from a long-term prospective, relatesto the concept of “crystal engineering” in the fabrication of such devices. Here, inorganic materialswill themselves be engineered totally on the nanometerscale, with the ultimate goal being the deliberatemanufacture of electronic band structures fully tailored to the particular device application. In this context, metal-loaded zeolites have recently been identified [2] aspotential candidates in the search for a dense bundle of quasi one-dimensional wires. This intriguing proposal, emanatin g from a major figure in the science and application of electronic devices, dovetailswith our own interestin the possibility of a compositionally-induced insulator-to-metal transition in alkali metal-loaded zeolites. In recent work we have highlighted the possibility that through the controlled introduction of alkali metals into the one-dimensional channels of zeolite L, it may be feasible to engineer genuine charge (electron)transport along the channels. Our goal is to producetotally engineered materials comprising a precise mesoscopic assembly of ultrafine atomic-scale conductingwires embedded within an insulating aluminosilicate host framework. In this paper, we report preliminary conductivity measurements on a series of potassium-loaded zeolite L samples. We examine the results of these physical measurements as a function of potassium composition as they approach the insulator-metal transition; the nature, origin and location of this electronic phase transition will underpin the search for such a dense bundle of metallic quasi one-dimensional wires. Keywords: “Crystal engineering”; Quasi one-dimensional metallic wires; Metal-loaded zeolites 1. Introduction The class of crystalline aluminosilicates known as zeolites, many of which are naturally occurring miner- als, are composed of corner-sharing Si04 and AlO tetrahedra, arranged into a three-dimensional frame- work in such a manner that they contain regular chan- nels and cavities of molecular dimensions (Fig. 1). Conventionally, a metal is often described as a regular array of ions embedded in a sea of itinerant electrons. Although neither exists in practice, a close approxima- tion to the former is a dehydrated zeolite such as zeolite L where cations, co-ordinated on only one side to an * Corresponding author. Tel.: 44 (0)121 414 4397. Fax.: 44 (0)121 414 4442. E-mail: P.P.Edwards@bham.ac.uk. anionic framework, line the inside of a series of regular channels. The controlled and continuous doping of “excess electrons” into these white, electrically insulat- ing solids is possible through their reaction with alkali metal vapour. Incoming alkali metal atoms are ionised by the intense electric fields existing within the zeolite, releasing electrons to interact with the zeolite cations [3-Q. We have noted that at some critical stage of metal loading, one expects enhanced electron-electron interactions and the possibility of an insulator-metal transition [&lo]. The primary purpose of this study is to examine the electrical conductivity of these metal-loaded zeolites as a function of potassium concentration and to determine whether the conduction mechanism ever att,ains metallic properties. Since the samples are both air and moisture sensitive, and in powder form, a contactless conductiv- 0921-5093/96/$15.00 0 1996 - Elsevier Science S.A. All rights reserved Pff SO921-5093(96)10352-X