X-Ray photoelectron spectroscopy has been used to study a series of iron oxides. It has been shown that iron metal has a different ionisation energy from a number of iron(ll1) oxides. Small perturbations to the energy of the iron(ll1) 2p electrons can be attributed to changes in crystal structure. Multiplet splitting and shake-up in the iron oxides contributes to iron 2p peak widths. The chemisorption of water has a marked effect upon the observed peak profiles ; the oxygen 1 s peaks due to oxide, hydroxyl, and adsorbed water have been characterised.ing Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire G L13 9PB A NUMBER of compounds containing iron and oxygen have been examined by X-ray photoelectron (X.1i.e.) spectroscopy. The inaterials were chosen to reflect the change in electronic environment of atoms on going from simple binary oxides t o ternary oxides incorporating various alkali metal atoms.The difficulties of surface contamination due to chemisorption, particularly of water, experienced in an earlier study of chromium-oxygen systems were again evident. ,&o, the resulting spectra were highly complex due to multiplet splitting effects which are characteristic of such iron compounds. EXPERIMEKTALMaterials and Reagents.-Lithium ferrite was prepared i n its face-centred cubic phase modification by the reaction of AiialaR lithium carbonate with Specpure Grade a-Fe,O,. The reaction mixture (having a Li,CO, : Fe,O, molar ratio of 1.03 : 1 rather than 1 : 1 t o compensate for vaporisation of Li,O during the reaction) was ground intimately, compressed into pellet form, and fired in a platinum crucible a t 900 K for 48 h in a stream of dry oxygen-free argon.The powder S-ray diffraction pattern for the reaction product was in excellent agreement with that given by Anderson and Schieber and analyses for lithium and iron showed deviations within only 1% from the required 1 : 1 atomic ratio.Sodium ferrite was prepared in its hexagonal a-phase modificatioii by the reaction of an intimate mixture of NaOH : Fe,O, in 2 : 1 molar ratio. The reactants were heated to 620 K (above the m.p. of KaOH) in a platinum crucible under a stream of dry oxygen-free argon. 2SaOH + Fe,03 _t BNaFeO, + H20The poudcr X-ray diffraction pattern given by the orange-brown reaction product was in excellent agreement with that published by Thkry and Collongues for a-NaFeO 2.The orthorhombic F-phase of sodium ferrite and facecentred cubic potassium ferrite were each prepared by the reaction of the corresponding alkali metal carbonate with Fe,O,. I n both cases the reaction mixture, in pellet form, was fired i n ; I nickel crucible at 1175 K for 48 h in a stream of dry oxygen-free argon. The product of each reaction gave a pon-tler X-ray diffraction pattern in excellent agreement with data in the literature [Watanabe and Fukase (for P-NaFeO,) and Barth (for KFeO,)].Wiistite, ' FeO ', was prepared by the reaction of Fe,O,

Recent results with solid-state semiconductor gas sensors based on organic sensor elements are reviewed. Devices based on metal phthalocyanines show useful responses to NO,. Lead phthalocyanine combines the highest conductivity with the maximum sensitivity to NO,. A thin-film lead phthalocyanine sensor has successfully been used to monitor NO, produced by shot-firing in coal mines. To obtain reasonable conductance and speed of response and recovery, phthalocyanine sensors have been operated at 170 "C. Conducting polymer materials, and particularly chemically doped polypyrrole, show responses to toxic gases at ambient temperature. Initial work, using polypyrrole black impregnated filter paper, showed a response to ammonia. More recently, using polypyrrole films electrochemically deposited over electrode arrays, responses to nitrogen dioxide and hydrogen sulphide have also been obtained. Organic-semiconductor gas sensors may have advantages compared to metal-oxide devices in their sensitivity to toxic gases and in their ability to operate at or near room temperature. However, the mechanisms of device function are not yet well understood.

The single-crystal material has a resistivity at 300 degrees C of 4.7 Omega cm and an activation energy of 0.13 eV. In the polycrystalline case it has been possible to separate out the bulk and grain boundary contributions to the total electrolyte resistance. These have activation energies of 0.15 and 0.26 eV respectively. The grain boundary or intergranular contribution becomes negligible above 200 degrees C and the sample resistivity at 300 degrees C is 15.4 Omega cm. The resistivity results obtained were independent of the electrode material used although this did affect the measured interfacial capacitance.

X-Ray photoelectron spectroscopy has been used to study a series of chromium-oxygen compounds. It has been shown that the ionisation energy of the chromium 2p electrons is dependent primarily on the oxidation state of the chromium metal ion, but that small perturbations may be attributed to changes in crystal structure and hence the Madelung potential. Multiplet splitting in chromium(iii) compounds contributes to peak widths, and the chemisorption of water and oxygen has a marked effect on the observed peak profiles. In addition such chemisorption apparently contributes to the build up of surface charge, thereby complicating the precise determination of binding energies.WE report here a study in which X-ray photoelectron spectroscopy l y 2 has been used to monitor tlie behaviour of chromium and oxygen atoms in a series of chromium conipounds. Several studies of chromium compounds have appeared in the For example, Hendrickson et aL3 have reported values of the binding energy of the chromium 3p shell in a wide range of compounds including some oxides and several complexes. In an attempt to resolve tlie two expected oxygen lines in dichromate (vr) compounds, Brundle and Robin4 investigated the spectrum of sodium dicliromate(v~) but reported only a single peak. The very

A series of experiments is described in which radio-tracer Zn was diffused into n-type InP over a wide range of experimental conditions. Diffusions were carried out in the temperature range 650-900 "C, for varying times of diffusion, and for a varicty of ambient vapour pressures. Both chemical and isoconcentration diffusions were performed, and it was found that the diffusion constants for chemical diffusion are much smaller than those for isoconcentration experiments. A detailed consideration of the shapes of the profiles shows that a time-dependent process occurs in the diffusion, giving rise to a concave section in some of the profiles. A model is proposed in which most of the Zn occurs in the InP in the form of the complex ( VpZnInVp). Zn atoms also occupy In sites, giving rise to the observed p-type conductivity and, in addition, exist in a fastdiffusing interstitial state. It is shown that the results of this and of previous work are in good qualitative agreement with the model.