Mirosław Kozłowski

Lattice parameters and orthorhombic distortion of CaMnO3

CaMnO3 is a parent compound for numerous multicomponent manganese perovskite oxides. Its crystallographic data are of primary importance in the science and technology of functional CaMnO3-based materials. In the present study, data were collected for a CaMnO3 sample at 302 K. The crystal structure refinement yields accurate absolute values of lattice parameters, a =5.281 59(4) angstrom, b=7.457 30(4) angstrom, and c=5.267 48(4) angstrom, leading to orthorhombic distortion of (c/a, root 2c/b) = (0.997 33 0.998 95). The orthorhombic distortion of the CaMnO3 structure is discussed on the basis of comparison Of Our unit-cell size with data already published. At a graphical representation of the distortion, it is observed that there is a considerable scatter of the distortion values among the literature data but, interestingly, a considerable fraction of experimental results (including the present one) for stoichiometric samples are grouped around the distortion (c/a, root 2c/b)=(0.9973,0.9990), which lies close to a maximum in the extent of orthorhombicity. The influence of off-stoichiometry on the orthorhombic distortion is discussed on the basis of available experimental data. Simulations, employing a mean-field approach for low temperatures, predict an increase in cell volume and structural distortions with the concentration of oxygen vacancies when the additional electrons are localized on the manganese. A simple model of delocalization produced the opposite effect, which is expected to combine with lattice vibrations to recover the cubic phase at high temperatures

Stable preparation of yeast mitochondria and mitoplasts synthesizing specific polypeptides

Yeast mitochondria isolated in the presence of 0.6 M sorbitol and 0.5% bovine serum albumin can be stored in liquid nitrogen without loss of translational activity. Frozen mitochondria retain the respiratory control and the mutant pattern of polypeptide synthesis identical to those detected for fresh preparations. Stored mitochondria may be efficiently transformed into a stable preparation of mitoplasts actively synthesizing mitochondrial polypeptides.

Protein synthesis in mitochondria from yeast strains carrying nam and mim suppressor genes

Yeast mitochondria isolated from two different wild type strains (gal+ and gal-), whether grown on galactose or glucose, synthesize all mitochondrial polypeptides with similar efficiencies and in proportions approximating those detected in vivo. Mitochondria isolated from mit- mutants synthesize in vitro a mutant pattern of mitochondrial proteins, indistinguishable from the in vivo products. The mutant pattern is restored to the wild type one in mitochondria isolated from pseudorevertant strains carrying an additional nuclear (nam3-1 and R705) or mitochondrial (mim3-1) informational suppressor gene. Suppression is expressed in isolated mitochondria without the obligatory presence of cytosol at the level of both respiratory control and specific polypeptide synthesis. Translation in isolated mitochondria is sensitive to paromomycin. The antibiotic differentiates between translation in mitochondria from wild type strains and that in nam-type gene carrying strains. This strongly suggests that nam-type mutations affect the mitoribosome, enhancing ambiguity of translation, thus allowing for the pseudoreversion of mit- phenotypes.

Investigation of Pd content in C–Pd films for hydrogen sensor applications

Nanocomposite carbonaceous-palladium (Nc-C-Pd) films were synthesized by physical vapor deposition method (PVD). Scanning electron microscopy studies showed that they were composed of carbonaceous matrix containing Pd nanograins. Nc-C-Pd films were also characterized by thermogravimetric analysis, X-ray powder diffraction, and Fourier transform infrared (FTIR) spectral analysis. The content of Pd in films synthesized at different PVD conditions was determined based on TG measurements. Technological parameters of PVD process affected C/Pd ratio. FTIR spectra exhibited characteristic absorption bands for the precursors of carbonaceous-palladium samples (fullerene C60 and palladium acetate). The influence of hydrogen on electrical properties of the films was tested by measuring their resistance in the presence of hydrogen (1% H2/N2).

Tem and CL Investigations of Pd Nanograins Included in Carbonaceous Film

In this paper we presented results of investigation of carbonaceous-palladium materials obtained in the CVD (Chemical Vapor Deposition) process. This investigations were carried out with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), equipped with spectrum imaging for cathodoluminescence (CL). The composites will be applied as a active layers in hydrogen and also hydrocarbons detectors. Our measurements showed that some of Pd nanoparticles have a graphite shell and also are optically active. This particle in CL spectrum reveal the peak wavelength around 525 nm (2,36 eV).

The Influence of Technological PVD Process Parameters on the Topography, Crystal and Molecular Structure of Nanocomposite Films Containing Palladium Nanograins

Abstract The paper describes the preparation and characteristics of films composed of Pd nanograins placed in carbonaceous matrix. Films were obtained in PVD (Physical Vapor Deposition) process from two sources containing: the first one - fullerene powder and the second one - palladium acetate. The topographical, morphological and structural changes due to different parameters of PVD process were studied with the use of Atomic Force Microscopy and Scanning Electron Microscopy, whereas the structure was studied with the application of the Transmission Electron Microscopy and Fourier Transform Infrared Spectroscopy methods. It was shown that topographical changes are connected with the decomposition ratio of Pd acetate as well as the form of carbonaceous matrix formed due to this decomposition. Palladium nanograins found in all films exhibit the fcc structure type and their diameter changes from 2 nm to 40 nm depending on the PVD process parameters.

Secondary electron microscopy and transmission electron microscopy studies of carbon nanotubes in C-Ni films

Carbon nanotubes films have been studied with SEM and TEM. The studied films were obtained using a two step method: PVD process and CVD process. Strongly defected and curled carbon nanotubes containing Ni nanoparticles formed the film with thickness of about 300–400 nm. Observed carbon nanotubes were of lengths from 100 nm to 300 nm and did not stick to each other.

Determination of sorption properties, total heterogeneity, and fractal dimensions of carbon nanotubes

Using special thermogravimetry and sorptometry methods physicochemical properties of carbon nanotube surfaces were investigated. A numerical and analytical procedure for the evaluation of total heterogeneous properties on the basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium conditions are presented. The desorption energy distribution was derived from the mass loss Q-TG and the differential mass loss Q-DTG curves of thermodesorption of pre-adsorbed polar and apolar liquid films. It is shown that the samples are highly sensitive to benzene vapor because the mechanism of liquid adsorption depends largely on the active surface centers and molecular interactions. For the first time, the evaluation of the fractal dimensions of nanotubes using the sorptometry and thermogravimetry data is presented.

Changes in the Structure of Palladium Nanograins in the Carbon Film (C-nPd) under the Influence of Hydrogen

Carbonaceous – nanopalladium (C-nPd) films on insulating substrates, obtained by PVD (Physical Vapor Deposition) followed by the annealing method, are used for hydrogen sensors. In this paper we present the results of XRD, SEM and electrical measurements of C-nPd films grown by PVD and then either annealed in an inert atmosphere or modified by CVD (Chemical Vapor Deposition). The structure of palladium grains were measured in a H2/N2 gas mixture atmosphere containing H2 in the concentration range 0-4%. Our measurements showed that C-nPd films prepared by PVD and annealing method were flat and they consisted of sphere-like palladium nano-particles, uniformly distributed in the low-ordered carbon matrix. Effect of hydrogen partial pressure on the crystal structure was studied in situ in GIXD measurements, using a specially designed measuring holder cell. It was observed that at low partial pressure of hydrogen, palladium fcc metal particles transformed into solid solution Pd(H) (α-phase), which occurs in the fcc structure as well. Lattice constant of that solid solution increases with increasing hydrogen partial pressure in the gas atmosphere. After exceeding the critical value of the partial pressure of hydrogen, palladium transforms into the structure of palladium hydride PdHx (β-phase), which has significantly larger lattice constant. This critical value of hydrogen partial pressure depends on the initial structure of C-nPd film, and consequently on the parameters of PVD process and annealing. This value usually corresponds to a few percent hydrogen content in gas mixture.

Properties of hydrogen sensitive C-Pd films obtained by PVD/CVD method

Structural, topographical and morphological changes of carbonaceous-palladium (C-Pd) films obtained by physical vapor deposition /chemical vapor deposition (PVD/CVD) method were studied. Effect of changes in these properties under the influence of CVD process temperature on the hydrogen sensitivity of these films is discussed. Scanning electron microscopy (SEM) observations were used to investigate the topography and morphology of an initial (PVD) film and the film modified in CVD process (PVD/CVD film) at different temperatures. The changes of film’s morphology after modification performed at various temperatures (500, 550, 600, 650, 700 and 750°C) caused changes in their resistance. The electrical measurements carried out in the presence of gas containing 1vol % of hydrogen showed different sensing characteristics for various films. The highest hydrogen sensitivity and the fastest response were observed for films modified at the temperature of 500°C and 550°C. In SEM images on surface of these films palladium nanograins with different sizes were observed. For films modified at the temperatures higher than 600°C Pd nanograins placed under superficial very thin carbonaceous layer were found.