W.S. Glaunsinger

Synthesis and characterization of small platinum particles formed by the chemical reduction of chloroplatinic acid

Abstract The preparation of platinum particles by the chemical reduction of chloroplatinic acid has been investigated in detail. The morphology and size of the product depends on the nature of the reducing agent, the presence and type of protective agent, and the reduction conditions. By carefully controlling these parameters, platinum spheres (⋍20–30 A diam), strands (⋍60 A diam), and composites (⋍100–200 A) can be synthesized. Polyvinylpyrrolidone was found to be the optimum protective agent due to its low protective ratio and high purity. The distribution of particle diameters for the spherical particles can be described by a log-normal distribution function. This work lays the foundation for studies of the chemical and physical properties of these particles. The applicability of this chemical-reduction approach to other systems is also outlined.

Magnetic properties of the semiconducting lanthanide cuprates Ln2CuO4 and their interpretation: evidence for a new series of planar copper antiferromagnets

Abstract The magnetic susceptibility of the semiconducting lanthanide cuprates Nd 2 CuO 4 , Pr 2 CuO 4 , Eu 2 CuO 4 , and Sm 2 CuO 4 has been measured in the range 4–300 K. Below 300 K, the Cu 2+ ions are ordered antiferromagnetically in the CuO 2 planes of these compounds, and the exchange interactions involving the Ln 3+ ions are relatively weak. The suceptibility of the Ln 3+ ions obeys the Curie-Weiss law at elevated temperatures, but deviations from this law occur at lower temperatures. An attempt is made to account for these deviations by fitting theoretical expressions for the susceptibility of isolated Ln 3+ ions under the influence of a cubic crystal field to the experimental data. Excellent agreement is obtained for Nd 3+ and Eu 3+ over the entire temperature range and for Pr 3+ and Sm 3+ at elevated temperatures. Deviations at lower temperatures for the latter two ions may be due to structural changes, exchange interactions involving the Ln 3+ ions, or possibly oxygen nonstoichiometry. The susceptibility parameters derived by fitting the theoretical expressions to the experimental data are also discussed. It is concluded that these compounds form an interesting new series of planar Cu 2+ -ion antiferromagnets.

Electrical, magnetic, and EPR studies of the quaternary chalcogenides Cu2AIIBIVX4 prepared by iodine transport☆

Abstract Electrical, magnetic, and electron paramagnetic resonance (EPR) measurements have been made on crystals and powders of several quaternary chalcogenides of the type Cu2AIIBIVX4, where AII = Zn, Mn, Fe, or Co, BIV = Si, Ge, or Sn, and X = S or Se. The electrical properties of these compounds are extrinsic, but their magnetic properties do not appear to be affected by impurities. The magnetic moments of the Cu2MnBX4 compounds decrease with increasing covalency of the MnX bond, and those of Cu2FeGeS4 and Cu2CoGeS4 reflect an orbital contribution to the moment. Both the Weiss constants and magnetic ordering temperatures in these compounds show an evolution from antiferromagnetism to ferromagnetism with increasing separation between the moments. Magnetic measurements on single crystals of Cu2MnGeS4, Cu2CoGeS4, and Cu2FeGeS4 indicate that only the latter is anisotropic. EPR measurements on crystals and powders of Cu2ZnGeS4 doped nominally with 0.1% Mn reveal that Mn2+ experiences an axial distortion and that the bond ionicity is the same as in ZnS.

Electron paramagnetic resonance spectroscopy of spin-labelled cuticle of Centruroides sculpturatus (Scorpiones: Buthidae): Correlation with thermal effects on cuticular permeability

Abstract Cuticular phase transitions and molecular dynamics have been studied in the buthid scorpion Centruroides sculpturatus using the techniques of thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR). TGA studies of the cuticular permeability reveal discontinuous changes in thermal dependence of transcuticular water loss rates (transitions). The first transition occurs between 30–40 C and results in a small increase in water loss rate, whereas the second transition begins near 55 C and is accompanied by a large increase in water loss rate. EPR spectra of spin-labelled cuticle indicate that the epicuticular lipids are very mobile at ambient temperature, with the translational diffusion coefficient being about 5 × 10−6 cm2 sec at 22 C. and that the low-temperature transition is associated with an increase in mobility of the hydrocarbon chains of the epicuticular lipids. The high-temperature transition probably results from melting of the epicuticular lipids. The results of this study are discussed with reference to current models of the structure of the arthropod cuticle.

Synthesis and characterization of nearly stoichiometric titanium disulfide

Abstract Nearly stoichiometric titanium disulfide has been synthesized by direct reaction between the elements using an optimal procedure and characterized by thermogravimetric and chemical analyses, ammonia intercalation rate, magnetic susceptibility measurements, and X-ray diffraction. The most nearly stoichiometric TiS 2 that can be prepared is Ti 1.0021±0.0010 S 2 , so that a slight excess of titanium is always present. This excess titanium inhibits the initial opening of the van der Waals gap during ammonia intercalation. The small titanium excess is the primary source of conduction electrons in TiS 2 , which supports the view that TiS 2 is an extrinsic semiconductor rather than a semimetal.

Characterization of Pt microcrystals using high resolution electron microscopy

Abstract Small colloidal particles of platinum have been produced with and without a protective agent (polyvinylpyrrolidone), and have been studied by high resolution electron microscopy. Initially, the protected particles have been found to be single crystals in the size range 5–30 A. After continued beam exposure, the protective coatings effect is lost and the particles coalesce, forming both larger single crystals and multiply-twinned crystals. In contrast, a sample of the unprotected particles shows extensive initial linking and twinning, but no further beam-induced agglomeration.

Magnetic investigation of the intercalation compounds LixTiS2

Abstract The magnetization and magnetic susceptibility of ten Li x TiS 2 intercalation compounds have been measured in the ranges 4.2–350 K and ⋍ 0–25 kG. The metallic nature of these compounds originates from electron donation from Li to the TiS 2 conduction band. The temperature-independent paramagnetism observed below about 100 K is typical of a metal, but at higher temperatures the susceptibility exhibits a rather large positive temperature coefficient. The composition dependence of the susceptibility displays a distinct plateau in the region where Li + ions are expected to order and shows evidence that Li is not completely ionized for x ⪆ 0.8. The density of electronic states is estimated from the measured susceptibilities and compared to that predicted for a nearly-free-electron metal as well as for other band structures, with the latter providing much better agreement with experiment. The results of this study clearly demonstrate that the rigid-band model is an oversimplification.

Deintercalation and reintercalation energetics of ammoniated titanium disulfide

Abstract The deintercalation and reintercalation processes in ammoniated TiS2 have been studied by thermogravimetric analysis, differential scanning calorimetry, vapor-pressure measurements, and powder X-ray diffraction. The enthalpies determined calorimetrically for complete NH3 and NH+4 deintercalation of (NH+4)0.24(NH3)0.23TiS0.24−2 are approximately 10.5 and 22 kcal/mole, respectively. These enthalpies are in good agreement with those reevaluated from a previous calorimetric study of ammoniated TaS2. Ammonia vapor-pressure curves for deintercalation and reintercalation of (NH+4)0.24(NH3)y″TiS0.24−2 exhibit hysteresis, and the enthalpies for these reactions are estimated to be 15.5 and −13 kcal/mole, respectively. The absolute values of these enthalpies decrease progressively as NH3 is deintercalated and then reintercalated. The structural changes that accompany these processes are relatively complex and involve at least two phases. Further structural studies are necessary to help elucidate the energetics of these intercalation compounds.

Magnetic properties of the mixed-valence compounds CaMn3O6 and CaMn4O8

Abstract The preparation of two new mixed-valence compounds, CaMn3O6 and CaMn4O8, are described and their magntic and EPR behavior investigated. The Mn moments in both compounds have nearly spinonly values. CaMn3O6 and CaMn4O8 order ferrimagnetically near 3 and 89 K, respectively. The broad, Lorentzian EPR lines indicate a significant exchange interaction between Mn3+ and Mn4+ ions. The magnetic and EPR results suggest a strong ferromagnetic interaction between Mn3+ and Mn4+ ions and a comparable antiferromagnetic Mn3+Mn3+ and/or Mn+Mn4+ interaction.

Ammonia oxidation and charge compensation in the metal ammonia intercalates Li+x(NH+4)y′(NH3)y″TiS(x+y′)−☆

Abstract The lithium-ammonia intercalates of TiS2, Li+x(NH+4)y′(NH3)y″TiS(x+y′)−, where 0.00 ≤ x ≤ 0.20, have been investigated by thermogravimetric analysis (TGA), vapor pressure measurements, X-ray powder diffraction, and SQUID magnetometry. TGA and vapor-pressure measurements indicate that ammonia deintercalation occurs by a distinct two-step process consistent with the ionic nature of these compounds. These materials are monophasic and crystallize in a 3R-type structure. The c lattice parameter increases linearly with increasing ammonia content, which may be associated with the diminution of the ion-dipole interaction of the cation(s) with the lone pair of ammonia. Compositional analysis by TGA shows that charge compensation occurs such that the total cationic concentration (x + y′) is constant at 0.22 ± 0.02. The Pauli paramagnetism of the conduction electrons corresponds to complete ionization of both lithium and ammonium, so that the driving force for the charge-transfer phenomenon is the transfer of 0.22 ± 0.02 electrons to the conduction band of TiS2. The degree of NH3 oxidation depends upon the relative intercalation rate of metal and NH3.