Showing papers on "Lattice constant published in 1968"
TL;DR: The Ferroelectric Ba0.27Sr0.75Nb2O5.78 as discussed by the authors is a tungsten bronze-type structure crystallizing in the tetragonal system, with lattice constants a = 12.43024
Abstract: Ferroelectric Ba0.27Sr0.75Nb2O5.78, with Tc = 348° ± 15°K, is a tungsten bronze‐type structure crystallizing in the tetragonal system, with lattice constants a = 12.43024 ± 0.00002 and c = 3.91341 ± 0.00001 A at 298°K, space group P4bm, and five formulas in the unit cell. The integrated intensities of 6781 structure factors were measured with PEXRAD, 875 symmetry‐independent structure factors being significantly above background. The metal‐atom positions were determined from the three‐dimensional Patterson function and the oxygen atoms from subsequent Fourier series. The final agreement factor between measured and calculated structure factors is 0.0508. The structure consists of close‐packed slightly puckered layers of oxygen atoms separated by nearly c / 2. The Nb atoms are slightly displaced from one layer, the Ba and Sr atoms from the other and in the same sense. The oxygen atoms in the Ba and Sr layer are disordered. Neither of the two independent sites occupied by the Ba and Sr atoms is fully filled....
570 citations
TL;DR: The preparation of crystals of bovine liver catalase, and their use as an internal standard of length in electron microscopy, are described and a critical appraisal of all available data suggests a figure of 172±4 A for the principalCatalase lattice spacing.
423 citations
TL;DR: In this paper, it was shown that there exists a composition domain for the lithium metaniobate near the stoichiometric compound Nb2O5-Li2O in the vicinity of the NbLiO3 compound.
368 citations
TL;DR: In this article, the solubility of MgTiO3 in Al2O3 was measured as 1.10 × loW4, 3.00 × 10”4, 6.80 × 10−4, and 1.40 × 10-3 at 1530, 1630°, 1730° and 183O°C, respectively.
Abstract: On heat treatment in air the solubility of MgO or TiO2, in Al23 is too small to detect by lattice parameter shifts. The solubility of MgTiO3 in Al2O3 in air increased to the measured values, expressed as atomic fractions Mg:A1or Ti:A1of0.82 × lo-2, 1.43 × 10-2, and 1.75 × 10-2 at 1250°, 1650°, and 1850°C, respectively. In 1 atm hydrogen the TiO2 solubility expressed as the atomic fraction Ti:A1 is 0.55 × lo-2, 0.75 × 10W2, 1.15 × 10-2, and 1.50 × 10p2 at 1400°, 1500°, 1600°, and 1700°C, respectively. The increased solubility in H2 was attributed to reduction of the titanium ion. The solubility of MgO in A12O3 in vacuum (0.3μ)expressed as the atomic fraction Mg:A1 was measured as 1.10 × loW4, 3.00 × 10”4, 6.80 × 10–4, and 1.40 × 10-3 at 1530°, 1630°, 1730°, and 183O°C, respectively. These contents did not cause an observable change in lattice parameter, but a slight change was observed when MgO was dissolved in A12O3 in a hydrogen atmosphere.
155 citations
TL;DR: Cobalt was deposited in ultra-high vacuum onto (001) copper surfaces prepared inside the vacuum chamber and the structure and lattice parameter of the cobalt remained the same as the copper until its thickness reached about 20 A. Many of these dislocations were unusual in that they were imperfect.
Abstract: Cobalt was deposited in ultra-high vacuum onto (001) copper surfaces prepared inside the vacuum chamber. If the copper substrate was at room temperature during film growth then the cobalt grew approximately as a monolayer. The structure and lattice parameter of the cobalt remained the same as the copper until its thickness reached about 20 A. At this thickness long dislocations to accommodate part of the difference between the lattice parameters of cobalt and copper were generated. Many of these dislocations were unusual in that they were imperfect. The stacking faults associated with them converted a little of the f.c.c. cobalt into the stable h.c.p. structure. If the copper was hot (350°C) during the deposition of cobalt, then film growth began with the formation of three-dimensional nuclei. Nuclei less than about 375 A in radius were f.c.c. and were strained to match the copper lattice.
146 citations
TL;DR: In this paper, lattice parameter data for MgO, CaO, and several isotropic compositions of LiH were measured from 12°K up to 300°K. Thermal expansion coefficients were derived by fitting the data to a second-degree polynomial.
Abstract: Lattice parameter data for MgO, CaO, and several isotropic compositions of LiH were measured from ~ 12 °K up to ~ 300 °K. Thermal expansion coefficients were derived by fitting the data to a second-degree polynomial.
133 citations
TL;DR: In this article, the flux line lattice in a type-II superconductor in the remanent state is investigated by means of a decoration method, where the triangular lattice contains various kinds of defects, the most important of which are flux line dislocations.
Abstract: The flux‐line lattice in a type‐II superconductor in the remanent state is investigated by means of a decoration method. The triangular lattice contains various kinds of defects, the most important of which are flux‐line dislocations. A critical lattice parameter dc exists such that for lattice parameters d>dc the flux lines form no longer a lattice but a ``flux‐line fluid.'' A belt directly underneath the specimen surface is free from flux lines. The transition from the ``fluid'' to the flux‐free region has been utilized to estimate in a fairly direct way the pinning forces acting on the flux lines.
115 citations
TL;DR: In this paper, the atomic configuration around a vacancy in aluminium and copper and the interaction energy between two vacancies in these metals were calculated using a harmonic discrete face-centred cubic lattice with first and second-neighbour interactions.
Abstract: The method of lattice statics is used to calculate the atomic configuration around a vacancy in aluminium and copper and the interaction energy between two vacancies in these metals. The model used is a harmonic discrete face-centred cubic lattice with first and second-neighbour interactions. The force constants are chosen to fit the elastic constants and phonon dispersion data for both aluminium and copper.
92 citations
TL;DR: A correlation between the lattice parameter and the carbon concentration in otherwise pure samples of silicon has been observed as discussed by the authors, and typical values of carbon concentration are given for some float-zoned silicon crystals and for a series of intentionally carbon-doped crystals.
Abstract: A correlation between the lattice parameter and the carbon concentration in otherwise pure samples of silicon has been observed. Carbon content has been determined by mass spectrometry, infrared, and lattice parameter measurements. Typical values of the carbon concentration are given for some float‐zoned silicon crystals and for a series of intentionally carbon‐doped crystals.
90 citations
TL;DR: In this paper, the lattice parameter a0 of thin single crystals of molybdenum disulphide was shown to be independent of crystal thickness and to have the value 31475 A at 293°K.
Abstract: The lattice parameter a0 of thin single crystals of molybdenum disulphide was shown to be independent of crystal thickness and to have the value 31475 A at 293°K. The variation of a0 with temperature was measured from 77 to 373°K.
88 citations
TL;DR: In this article, the third-order term in the pseudopotential expansion of the total energy of the ions and conduction electrons has been derived, which is a structural expansion of cohesive energy valid for an arbitrary arrangement of the ion.
Abstract: In the modern theory of simple metals a large number of physical properties, such as the cohesive energy, lattice constants, lattice structure, elastic constants and vibration spectra are calculated from a self-consistent pseudopotential expansion of the total energy of the ions and conduction electrons. This expansion, which is actually a structural expansion of the cohesive energy valid for an arbitrary arrangement of the ions, has only been known to second order. In the present paper the third-order term in this expansion is derived.
TL;DR: Lattice spacings have been determined at room temperature for the cubic (C15) Laves phases formed by rare-earth metals with iron, and with nickel, together with the variation of lattice spacing with temperature for GdCo 2.
Abstract: Lattice spacings have been determined at room temperature for the cubic (C15) Laves phases formed by rare-earth metals with iron, and with nickel, together with the variation of lattice spacing with temperature for GdCo 2 The results are briefly discussed and compared with previous work on GdCo 2 The results suggest that in GdFe 2 and GdNi 2 the gadolinium atoms have an abnormally small apparent atomic diameter, whereas in GdCo 2 , the apparent atomic diameter of gadolinium corresponds with that of the pure metal In CeFe 2 , CeCo 2 , and CeNi 2 the apparent atomic diameters of cerium are consistent with the complete or partial transfer of the 4 f electrons of cerium to the conduction band The elements samarium, neodymium and praseodymium appear to adopt expanded atomic diameters in the RENi 2 phases similar to those observed in the corresponding REAl 2 and REPt 2 phases
TL;DR: In this paper, the cubic field was widened when CaCO2 was substituted for CaO as a reagent, probably because of the formation of an intermediate active oxide, which may shed light on some of the discrepancies in the literature.
Abstract: The range of existence of the cubic phase in the system CaO-ZrO2 was determined at temperatures from 1300° to 1700°C, using the lattice parameter method. This technique could not be used at higher temperatures because of anomalous changes in the lattice parameter. The possibility of the existence of a compound, CaZr4O9, occurring at 20 mole % CaO, was inferred from X-ray data. The (hypothesized) compound appeared to undergo a phase transformation at about 1650°C. The cubic field was widened when CaCO2 was substituted for CaO as a reagent, probably because of the formation of an intermediate active oxide. This widening of the field may shed light on some of the discrepancies in the literature.
TL;DR: A series of clathrates with the general formula M(NH3)2M′(CN)4.2G were prepared in this article, and their structures have been ascertained by powder X-ray diffractometry to be similar to that of Hofmann's clathrate Ni(NH 3)2Ni(CN 4.2C6H6.
TL;DR: A series of isomorphous compounds of composition R.E. 2 In has been prepared by alloying rare earths with indium as discussed by the authors, and the structure of these compounds corresponds to that of the Ni 2 In type.
Abstract: A new series of isomorphous compounds of composition R.E. 2 In has been prepared by alloying rare earths with indium. The structure of these compounds corresponds to that of the Ni 2 In type and is observed for all trivalent rare earths from La to Lu with the exception of Eu and Yb which do not form this phase. For Ho, Er, Tm and Lu the phase R.E. 5 In 3 was additionally found; this phase has the Mn 5 Si 3 type of structure which is closely related to that of Ni 2 In.
TL;DR: In this paper, X-ray diffraction experiments with poly(p-phenylene) pellets demonstrated an increase in crystallinity with increase in molding temperature or annealing temperature.
Abstract: X-ray diffraction experiments with poly(p-phenylene) pellets demonstrated an increase in crystallinity with increase in molding temperature or annealing temperature. The increase in crystallinity may be attributed to annealing effects and loss of chlorine under severe conditions. Lattice constants for the crystalline polymer are presented, and the crystallographic data are compared with those of the lower oligomers. Poly(p-phenylene) was investigated also in relation to oxidative thermal stability, chemical and solvent resistance, and the effect of temperature and variation in molding conditions on fracture strength. The decrease in strength at elevated temperatures appears to be related to the increase in crystallinity.
TL;DR: In this paper, a small amount of Ba or Sr is substituted for Pb in Pb(Mg1/3 Nb2/3)O3-PbTiO3 -Pb2rO3, and the morphotropic boundary and the compositions which show the highest planar coupling coefficient and dielectric constant shift slightly toward the decreasing Pb TiO3 content.
Abstract: When a small amount of Ba or Sr is substituted for Pb in Pb(Mg1/3 Nb2/3)O3-PbTiO3-Pb2rO3, the morphotropic boundary and the compositions which show the highest planar coupling coefficient and dielectric constant shift slightly toward the decreasing PbTiO3 content. The tetragonality of Pb(Mg1/3Nb2/3)O3-PbTiO3 and Pb(Mg1/2 Nb2/3)-O3-PbTiO3-PbZrO3 ceramics decreased with increasing Ba or Sr content. The lattice parameter (α axis) in the rhombohedral or pseudocubic phase increased with the increase of Ba but decreased with the increase of Sr substitution. Although the Curie temperature was lowered with the increase of Ba or Sr, the dielectric constants of the ceramics were increased. The dielectric and piezoelectric properties of the ternary compositions near the morphotropic boundary were improved through selection of sub-stituent and base composition. A planar coupling coefficient of 0.66 and a low Young's modulus were obtained with substitution of 5 mole % Ba. A dielectric constant greater than 3500 and a planar coupling of 0.63 can be obtained by substituting 5 mole % Sr.
TL;DR: In this paper, the Korringa-Kohn-Rostoker method was used to calculate the change in the electronic band structure of copper with change in lattice spacing.
Abstract: Calculations are described which relate to the change in the electronic band structure of copper with change in lattice spacing. The calculations were performed using previously described constant-energy search techniques based on the Korringa-Kohn-Rostoker method for band-theory calculations. Included in the results are a total of 26 066 points on each of three Fermi surfaces corresponding to lattice spacings $a$, $0.995a$, and $0.99a$, with $a$ being the normal lattice constant of copper. Using the measured value for the volume compressibility, our results give calculated changes in the Fermi surface with pressure which agree very well with recent de Haas-van Alphen experimental results. The calculated results are also consistent with the pressure dependence of reflectivity measurements, and with experiments thermodynamically related to the pressure dependence of the density of states at the Fermi energy. These results are based on band structures obtained from potentials calculated by a commonly invoked prescription using free-atom charge densities and Slater exchange. When considering the uncompressed metal, this prescription has been found to generate potentials giving widely varying band structures when different free-atom charge densities are used. However, once free-atom charge densities have been found which generate a reasonably accurate potential for the uncompressed metal, we conclude from the present results that the potential prescription appears to be very promising in its ability to accurately describe changes in metallic band structures with changes in lattice spacing.
TL;DR: In this paper, the magnetic properties of the series of pseudo-binary compounds YFeuCo2-u have been examined in an attempt to obtain further information concerning the nature of the transition-metal moment in the cubic Laves-phase rare-earth -transition-metal compounds.
Abstract: The magnetic properties of the series of pseudo-binary compounds YFeuCo2-u have been examined in an attempt to obtain further information concerning the nature of the transition-metal moment in the cubic Laves-phase rare-earth - transition-metal compounds. The variation of the observed moment throughout the series can be understood on the basis of a non-localized moment associated with the transition-metal ion. The variation of the Curie temperature may be associated with the variation of the lattice parameter between the terminal compounds.
TL;DR: In this article, the cation distribution of MnxZn1−xFe2O4 has been determined by neutron diffraction and it is concluded from the measurements that zinc ferrite is a completely normal spinel and that the Mn2+ ions only occupy the tetrahedral sites up to x = 0.6.
Abstract: The cation distribution of MnxZn1−xFe2O4 (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, 1.0) has been determined by neutron diffraction. The fraction of the Mn2+ ions in the tetrahedral sites is correlated to the variation of the lattice parameter with x. It is concluded from the measurements that zinc ferrite is a completely normal spinel and that the Mn2+ ions only occupy the tetrahedral sites up to x = 0.6.
TL;DR: The phase boundaries of the Zr-H system have been defined at high hydrogen concentrations, on the basis of studies performed on zirconium hydrides containing 4 at % uranium as discussed by the authors.
TL;DR: In this paper, the particle size dependences of the spin flip transition temperature (Morin temperature) and of the lattice constant of α-Fe 2 O 3 were studied experimentally.
Abstract: The particle size dependences of the spin flip transition temperature (Morin temperature) and of the lattice constant of α-Fe 2 O 3 were studied experimentally. With decreasing particle size, it was found that the Morin temperature shifts downwards and crystal lattice expands both in a - and c -axis directions. As the origin of the Morin temperature shift, the change of the dipolar magnetic field due to the lattice dilatation was considered. Experimental values were compared to the theoretical calculation of Artmann and a qualitative agreement was obtained.
TL;DR: In this article, the authors discuss the effect of crystal structure and lattice parameter effects on single and polycrystalline metals adhesion, friction and wear properties, and discuss basal slip hexagonal metals.
TL;DR: A micrographic study of some alloys of the Cu-Mn-Sb system in both the as-cast and heat-treated conditions, revealed the presence of a single phase alloy (lattice parameter, a = 6·088 ± 0·003 A ) at the composition CuMnSb as mentioned in this paper.
TL;DR: In this paper, a three-dimensional, classical study of gas-solid surface interaction phenomena is reported, where nine movable lattice sites are connected to fixed points by harmonic springs in a geometry chosen to represent either the (100) or (111) planes of a Ni crystal.
Abstract: A three‐dimensional, classical study of gas–solid surface interaction phenomena is reported. An independent‐oscillator lattice model is assumed to represent the crystal surface. Nine movable lattice sites are connected to fixed points by harmonic springs in a geometry chosen to represent either the (100) or (111) planes of a Ni crystal. The interaction potential is constructed from nine pairwise Morse potentials operating between the incident gaseous atom and the nine movable lattice points. Energy‐transfer coefficients (ETC) and spatial distributions are calculated as a function of incidence angle, gaseous beam velocity and temperature, surface temperature, gaseous atom mass, lattice force constant, and attractive well depth and curvature by numerical solution of the 60 differential‐motion equations. The results indicate that the ETC should decrease with increasing incidence angle, decreasing attractive well depth and curvature, increasing lattice force constant, and decreasing isotopic mass of the incident gaseous atom. As the surface temperature approaches and exceeds the gaseous beam temperature, the ETC is also predicted to decrease. The rate of decrease of the ETC with incidence angle seems sufficient to justify the normal component model in contrast to previous two‐dimensional results. Energy transfer is found to be favored for collisions near lattice sites. The calculated ETC values are virtually independent of the crystal plane being attacked. The calculated three‐dimensional spatial distributions exhibit peak maxima and half‐widths characteristic of experiment. The distributions are strongly dependent upon incidence angle and, under certain conditions, exhibit a “bimodal” structure. This structure is observed to decrease with increasing beam and surface temperatures, decreasing incidence angle, and decreasing attractive well. Subspecular shifts of calculated peak maxima are predicted for increasing surface temperature. The angular distributions in planes parallel to the surface are peaked at the in‐plane angle and decrease rapidly on either side of it. This effect becomes more pronounced as the incidence angle and the beam temperature are increased and as the attractive well depth is decreased. Insofar as comparison with experiment is possible, virtually all results are in qualitative to semi‐quantitative agreement with available experimental data.
TL;DR: A high-temperature x-ray study of pure iron has shown that a small but easily detectable, lattice parameter anomaly, representing a decrease in the mean linear thermal expansion coefficient, occurs over a narrow range of temperature (similar 35 degc) about the Curie point.
Abstract: A high-temperature x-ray study of pure iron has shown that a small, but easily detectable, lattice parameter anomaly, representing a decrease in the mean linear thermal expansion coefficient, occurs over a narrow range of temperature (similar 35 degc) about the Curie point. The total volume change associated with the ferromagnetic-paramagnetic transition in pure iron obtained from the experimental measurements gave values in good agreement with those calculated directly from volume magnetostriction data, although for an alternative method of calculation the agreement was poor.
TL;DR: The crystal structure of A12(WO4)3 has been determined in this paper, and it is known as 2AlaO3.5WO3, which is isomorphous with the tung states and molybdates of the smaller rare-earth elements.
Abstract: The crystal structure has been determined of a compound initially reported as having the composition 2A1203.5WO3. The final structure analysis proved the substance to be 2AlaO3.6WO3 or A12(WO4)3, and it is isomorphous with the tungstates and molybdates of the smaller trivalent rare-earth elements. A12(WO4)3 crystallizes in the orthorhombic system, space group Pbcn, with lattice constants a= 12.588 + 0.063, b = 9.055 + 0.045, c = 9.127 + 0.046 A. The intensities of three-dimensional equi-inclination Weissenberg data were estimated visually and the structure was solved by Patterson and Fourier techniques. Refinement of atomic parameters was carried out by the method of least-squares. The A12(WO4)3 structure consists of WO4 tetrahedra and A106 octahedra which extend into an infinite three-dimensional network by corner sharing. The average tetrahedral W-O distance is 1.783 (23) A and the average A1-O bond distance is 1-836 (35)A,. The structure contains discontinuous cubic face-centred anion units linked by corner-sharing polyhedra. A high density form of A12(WO4)3 is discussed, based upon a continuous cubic close-packed array of anions.
TL;DR: In this paper, the Korringa-Kohn-Rostoker method was used to construct the potentials for the noble metal bands at twelve points in 1/48th of the Brillouin zone.
Abstract: Band structures for the noble metals have been calculated at twelve points in 1/48th of the Brillouin zone by the Korringa-Kohn-Rostoker method. The bands were calculated at two values of the lattice constant for copper and silver and at one value for gold. The potentials used in this calculation were constructed by a method akin to that used by Abarenkov and Heine and by Animalu and Heine for the non-transition metals. The results are presented and compared with experiment.
TL;DR: In this paper, the formation of hexagonal and cubic forms of ice was studied by the use of a cold stage in an electron microscope within the temperature range −90° to −180° C.
Abstract: The formation of hexagonal and cubic forms of ice was studied by the use of a cold stage in an electron microscope within the temperature range −90° to −180° C. Ice crystal specimens were made on cold substrates, i.e. a collodion film, gold foil, or copper grid on the specimen holder of the cold stage. The hexagonal form of ice formed on the cold substrates at temperatures from−90° to−100° C. At −100° to −130° C, both hexagonal and cubic forms of ice were detected. From −130° to −160° C only cubic ice was found. At temperatures below −160° C, minute crystals of cubic ice were detected. No transformation of the structural form of ice from hexagonal to cubic or from cubic to hexagonal occurred when the temperature of the specimens was varied in the range −90° to −160° C. The lattice constants of hexagonal and cubic ice, and the coefficient of thermal expansion of ice were calculated from the experimental results.
TL;DR: In this article, the crystal structure of trans-1,4-polybutadiene has been revealed to belong to the monoclinic system with the space group P21/a.
Abstract: The crystal structure of trans-1,4-polybutadiene has been reported by Natta et al. to be pseudo-hexagonal below its solid-phase transition temperature. In the present X-ray structure analysis, it is revealed that the crystal belongs to the monoclinic system with the space group P21/a. The unit cell, with the lattice constants a = 8.63 A, b = 9.11 A, c = 4.83 A, and β = 114°, includes four molecular segments.