The structure of the rocking curves observed close to a dynamical n-beam point is described. Data recorded on the 16C NSLS X-ray beam from a perfect single crystal of Si[222] are presented. These data demonstrate rocking curves with two and in some cases three peaks, one at a fixed position and the others at different positions. Their position and intensity are a function of the distance from the n-beam interaction peaks.

Detailed (00L) neutron scattering profiles have been measured versus hydrostatic pressure (0P20 kbar) at room temperature for potassium-graphite intercalation compounds ${\mathrm{KC}}_{\mathrm{x}}$ with 8x40. The average density of filled galleries along the c axis decreases with increasing P, implying a concomitant increase in the (average) areal K density within a gallery. We observe both large P regions exhibiting continuous evolution of different stages, and narrow P regions where the average stage changes abruptly. The Hendricks-Teller model of one-dimensional disorder is used to fit entire diffraction profiles over extended q ranges. Some of the high-P staging and disorder effects are attributable to P-induced in-plane intercalate densification, the sequence of gallery occupancy and its perfection being a secondary consequence. Other features are entirely controlled by interlayer interactions: e.g., a pure stage-4 phase evolves asymptotically with increasing P at 6--7 kbar for 36x39, whereas a commensurate 2\ifmmode\times\else\texttimes\fi{}2 in-plane density would be compatible with a pure stage-4 phase only for x=32.0. We demonstrate from the fits that the fractional stage-(3/2) phase in ${\mathrm{KC}}_{8}$, reported earlier by us to occur between 15 and 19 kbar, exhibits c-axis correlations no worse than other high-P phases, indicating that this unusual structure represents a true equilibrium phase and does not result simply from random layer sequencing.

Time-resolved polarization measurements on BaTi${\mathrm{O}}_{3}$ for pressures between 1 atm and the tricritical pressure ${P}_{t}\ensuremath{\equiv}32$ kbar reveal a delay between the application of an electric field and the rise of polarization towards its equilibrium, ferroelectric value. The delay decreases exponentially with the difference between applied electric field and the field at which the equilibrium ferroelectric-paraelectric transition occurs. A model which includes long-range elastic and dipole interactions present in single crystals gives a qualitative description of the delay time.

A partial Meissner effect, fully diamagnetic shielding signals, and large anisotropies in the upper and lower critical fields in ditetramethyltetraselenafulvalene-hexafluorophosphate [${(\mathrm{TMTSF})}_{2}$P${\mathrm{F}}_{6}$] under applied hydrostatic pressure are observed.

High-resolution x-ray scattering studies show a new charge-density wave (CDW) structure on warming through the commensurate-incommensurate transition in $2H$-Ta${\mathrm{Se}}_{2}$ at 93 K. In contrast to the fully incommensurate CDW structure seen on cooling, hexagonal symmetry is broken in the new phase and the triple-$\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$ CDW has one commensurate and two incommensurate wave vectors. At 112 K (warming) the CDW transforms to the fully incommensurate structure.

The magnetic properties of modulated Cu-Ni films with Ni thickness ranging from 6 to 60 \AA{} and for various Cu thickness have been measured at room temperature, 77\ifmmode^\circ\else\textdegree\fi{}K, and 4.2\ifmmode^\circ\else\textdegree\fi{}K. The results show that the magnetic properties do not depend on the Cu thickness but only on the surface to volume ratio of the Ni. The Ni behavior is interpreted in terms of a large surface anisotropy, and not in terms of an enhanced moment.

Using neutron scattering techniques, we show that the destruction of superconductivity in Er${\mathrm{Rh}}_{4}$${\mathrm{B}}_{4}$ at ${T}_{c2}=1.0$ K is accompanied by the development of long-range ferromagnetic ordering of the Er sublattice. The observed magnetic Bragg intensities indicate that the Er ion has a moment of 5.6${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$ which is oriented in the tetragonal basal plane. The magnetic transiton appears second order, but shows anomalously strong precursor scattering.

It has been suggested that Yb and Sr undergo semimetal-to-semiconductor transitions under pressure. We have measured the electrical resistivity $\ensuremath{\rho}$ from 298 to 2\ifmmode^\circ\else\textdegree\fi{}K at different pressures up to 50 kbar. In Yb, $\ensuremath{\rho}$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K increases by a factor of 6\ifmmode\times\else\texttimes\fi{}${10}^{4}$ at $P=25$ kbar and saturates at higher pressures. For $P<25$ kbar, we find the empirical relation at 4.2\ifmmode^\circ\else\textdegree\fi{}K $\mathrm{ln}[\frac{\ensuremath{\rho}(P)}{\ensuremath{\rho}(1 \mathrm{atm})}]=0.45 P$, where $P$ is the pressure in kbar. At $P=25$ kbar, the resistance ratio $\frac{\ensuremath{\rho}({4.2}^{\ensuremath{\circ}}\mathrm{K})}{\ensuremath{\rho}({298}^{\ensuremath{\circ}}\mathrm{K})}=220$. In Sr the resistance rise is much less dramatic, $\ensuremath{\rho}$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K increasing by a factor of 50 in 35 kbar. A small negative temperature coefficient of resistivity appears for $P\ensuremath{\gtrsim}30$ kbar in Sr. We suggest that Yb becomes a semiconductor at high pressures, whereas Sr remains a semimetal. These conclusions are compatible with the band-structure calculations of Vasvari, Animalu, and Heine for the fcc alkaline-earth metals, if the effects of spin-orbit coupling are included. We find no evidence for either an excitonic phase or a first-order transition in the neighborhood of the semimetal-to-semiconductor transition at low temperatures. However, no definitive statements can be made because of impurity effects. The Yb sample was 99.99% pure according to emission-spectrographic analysis. At higher pressures both Yb and Sr showed the transition to the bcc phase, and in this phase both materials behaved as a good metal and showed no evidence of a magnetic transition.

A first-order metal-insulator transition at room temperature has been found in Cr-doped ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ as a function of both Cr concentration and pressure. This is shown to be a Mott transition in which the conduction electrons localize to form the insulator. A generalized phase diagram relating the metallic, insulating, and antiferromagnetic insulating phases is presented.

The N\'eel and Curie temperatures of some alloys of the heavy rare-earth metals with each other and with yttrium have been measured as functions of pressure up to \ensuremath{\sim}85 kbar. The initial slopes ($\frac{\mathrm{dT}}{\mathrm{dP}}$) are approximately proportional to the average de Gennes function ($\ensuremath{\Sigma}{i}^{}{c}_{i}{({g}_{i}\ensuremath{-}1)}^{2}{J}_{i}({J}_{i}+1)$). In the molecular field approximation with a first-order correction for the anisotropy energy, the change in the exchange interaction with lattice parameter is given by $\frac{{k}^{\ensuremath{-}1}dJ(\mathrm{Q})}{\mathrm{da}}=(42\ifmmode\pm\else\textpm\fi{}6)\ifmmode^\circ\else\textdegree\fi{}$K/\AA{}. It is suggested that this is caused mainly by a change in the generalized conduction-electron susceptibility with pressure. A polymorphic transition from a hexagonal-close-packed structure to a Sm-type structure is found with increasing pressure in many of these alloys, and the Sm-type phase has two ordering temperatures. The higher ordering temperature of the Sm-type phase is 10% lower than that of the hcp phase, and the two ordering temperatures in the Sm-type phase differ by 17%.

The N\'eel temperature of Cr is found to vary exponentially with volume, which is in support of a two-band model of itinerant antiferromagnetism. The temperature dependence of the magnetic contribution to the electrical resistivity can be explained by taking into account only the variation in the number of effective carriers from the introduction of a band gap ($2\ensuremath{\Delta}$) due to the magnetic ordering. The ratio $\frac{{\ensuremath{\Delta}}_{0}}{k{T}_{\mathrm{N}}}$ is estimated at 2.3 at $P=26$ kbar.

The change of the N\'eel temperature of europium metal and of the Curie temperature of EuO with pressure has been measured up to 90 kbar by resistivity and initial-permeability methods, respectively. The compressibility of Eu and EuO has been determined relative to NaCl in the same range of pressure by powder x-ray diffraction methods. The compressibility is represented by the Birch equation; for Eu ${B}_{0}=124$ kbar and $\ensuremath{\xi}=0.9 (\frac{d{\ensuremath{\beta}}_{0}}{\mathrm{dp}}=2.8)$ and the standard deviation is 1.8; for EuO, ${B}_{0}=1070$ kbar and $\ensuremath{\xi}$ was assumed to be zero and the standard deviation is 2.8. For Eu, $d\mathrm{ln}\frac{{T}_{N}}{d}\mathrm{ln}V\ensuremath{\approx}0$ down to $\frac{V}{{V}_{0}}=0.8$. The initial slope for EuO is $d\mathrm{ln}\frac{{T}_{c}}{d}\mathrm{ln}V=\ensuremath{-}6\ifmmode\pm\else\textpm\fi{}2$. The results are discussed in terms of the theories of exchange interaction in the heavy rare-earth metals and the europium chalcogenides.

X-ray diffraction powder patterns taken at high pressure suggest by analogy to Gd that Tb, Dy, and Ho have first-order transitions from a hcp to a Sm-type structure at high pressure. The $\frac{c}{a}$ ratio of the hcp phases increases with pressure toward the ideal value. The change of the Curie or N\'eel temperature with pressure of Gd, Tb, Dy, and Ho has been measured up to 85 kbar by an ac method in which the sample forms the core of a transformer. The first-order transitions are observed in changes in the magnetic properties. The initial susceptibility shows two new peaks in isobaric temperature cycles made above the transitions. The difference between the ordering temperature of the low- and high-pressure phases near the transition are -37, -21, -12, and -9\ifmmode^\circ\else\textdegree\fi{}K for Gd, Tb, Dy, and Ho, respectively. The change in the Curie point of Gd(I) is -1.72\ifmmode\pm\else\textpm\fi{}0.7\ifmmode^\circ\else\textdegree\fi{}K/kbar. The changes in N\'eel temperature are: Gd(II) -1.46\ifmmode\pm\else\textpm\fi{}0.11, Tb(I) -1.07\ifmmode\pm\else\textpm\fi{}0.03, Tb(II) -0.83\ifmmode\pm\else\textpm\fi{}0.08, Dy(I) -0.66\ifmmode\pm\else\textpm\fi{}0.04, Dy(II) -0.67\ifmmode\pm\else\textpm\fi{}0.07, Ho(I) -0.48\ifmmode\pm\else\textpm\fi{}0.01\ifmmode^\circ\else\textdegree\fi{}K/kbar. The results are compared with other measurements on rare-earth metals.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPRESSURE—TEMPERATURE—RESISTANCE PROPERTIES OF LANTHANUM, BISMUTH, NEPTUNIUM, PLUTONIUM, AND AMERICIUM TO 450° AND 30 KB.D. McWhan, P. W. Montgomery, H. D. Stromberg, and G. JuraCite this: J. Phys. Chem. 1963, 67, 11, 2308–2311Publication Date (Print):November 1, 1963Publication History Published online1 May 2002Published inissue 1 November 1963https://pubs.acs.org/doi/10.1021/j100805a013https://doi.org/10.1021/j100805a013research-articleACS PublicationsRequest reuse permissionsArticle Views122Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts