Magnetic susceptibility sample preparation

The magnetic susceptibility, measured with a vibrating sample magnetometer (Foner), calibrated with nickel (purity 99.99% — specific susceptibility at 293°K 55 cgs/g) at 293 0.2°K with a magnetic field of 17,700 G, is 101.39 0.20 10"6 cgs/g. This value may be compared with 101.65 0.20 10 6 cgs/g for manganese diphosphate prepared by thermal decomposition of the ammonium manganese phosphate. The value calculated from Reference 7 is 101.96 0.20 cgs/g. 

An examination of the magnetic susceptibility, thermal analysis characteristics, and X-ray powder patterns of samples of V02+ c( — 0.02 x < 0.03) prepared by heating V205-V203 mixtures in silica tubes has shown that the homogeneity range for V02 is very narrow.393"... 

The M-NM transition has been studied in powder samples (prepared by the ceramic method) of the series of perovskite oxides Lai- TiOs with 0 temperature dependencies to the magnetic susceptibility (Fig. 7.6a) and electrical resistivity (Fig. 7.6b) for different compositions, as well as the cell parameters for the phases ... 

Sample 1 was prepared with excess CsiPdFg and had less CsAsF6 impurity, since in this case it had lowered solubility because of the common ion effect of the highly soluble Cs2PdF6. Sample 3 is least reliable because it contains KAsF6 (seen in XRDP) and was small. In each case, the magnetic susceptibility obeyed the Curie law (Weiss constant 0 K). 

It was assumed that OsO,F, would be colourless and diamagnetic and phjrsically similar to OsOF, and OsF,. The infrared spectra of osmium oxide pentafluoride samples taken from a variety of preparations were identical with one another. The entire product from one oxyfluorination of osmium metal was subjected to infrared examination. The bulk of the sample in a Monel trap, was isolated from the gas cell by a Hoke valve. After each vapour sample had been scanned it was discarded and a new sample of vapour admitted. This was repeated exhaustively. All the spectra were interpretable in terms of OsF OsOF OsO and traces of HF, CF, SiF and CO,. Two independent magnetic measurements on samples of OsOF one from an oxjrfluorination of the metal and the other from the fluorination of the dioxide gave magnetic susceptibility values equal within the usual experimental uncertainty. Furthermore the magnitude of the susceptibility was consistent with pure OsOF,. 

NiO(250°) contains more metallic nickel than NiO(200°). Magnetic susceptibility measurements have shown that carbon monoxide is adsorbed in part on the metal (33) and infrared absorption spectra have confirmed this result since the intensity of the bands at 2060 cm-i and 1960-1970 cm-1 is greater when carbon monoxide is adsorbed at room temperature on samples of nickel oxide prepared at temperatures higher than 200° and containing therefore more metallic nickel (60). Differences in the adsorption of carbon monoxide on both oxides are not explained entirely, however, by a different metal content in NiO(200°) and NiO(250°). Differences in the surface structures of the oxides are most probably responsible also for the modification of their reactivity toward carbon monoxide. In the surface of NiO(250°), anionic vacancies are formed by the removal of oxygen at 250° and cationic vacancies are created by the migration of nickel atoms to form metal crystallites. Carbon monoxide may be adsorbed in principle on both types of surface vacancies. Adsorption experiments on doped nickel oxides, which are reported in Section VI, B, have shown, however, that anionic vacancies present a very small affinity for carbon monoxide whereas cationic vacancies are very active sites. It appears, therefore, that a modification of the surface defect structure of nickel oxide influences the affinity of the surface for the adsorption of carbon monoxide. The same conclusion has already been proposed in the case of the adsorption of oxygen. 

Removal of lattice oxygen from the surface of nickel oxide in vcumo at 250° or incorporation of gallium ions at the same temperature [Eq. (14)] causes the reduction of surface nickel ions into metal atoms. Nucleation of nickel crystallites leaves cationic vacancies in the surface layer of the oxide lattice. The existence of these metal crystallites was demonstrated by magnetic susceptibility measurements (33). Cationic vacancies should thus exist on the surface of all samples prepared in vacuo at 250°. However, since incorporation of lithium ions at 250° creates anionic vacancies, the probability of formation of vacancy pairs (anion and cation) increases and consequently, the number of free cationic vacancies should be low on the surface of lithiated nickel oxides. Carbon monoxide is liable to be adsorbed at room temperature on cationic vacancies and the differences in the chemisorption of this gas are related to the different number of isolated cationic vacancies on the surface of the different samples. 

In view of the recent Mbssbauer investigation, the differences in magnetic moments observed in previous studies are probably related to differences in the Co phase distribution which, in fact, has been found to be sensitive to the choice of preparation parameters. To avoid such ambiguities, it is thus necessary to measure the magnetic susceptibility on samples where the Co phase distribution is known. This will also allow one to obtain magnetic properties for the catalytically active Co-Mo-S species. 

Several samples of YBa2Cu307 x with controlled stoichiometries, 0.04 < x < 1.00, have been prepared and characterized by thermogravimetric analysis, differential scanning calorimetry, magnetic susceptibility and Meissner effect measurements. 

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