Research Development on Sodium-Ion Batteries

A. Water Exchange 2326 B. Proton Exchange 2327 C. Electronic Relaxation 2327 D. Relaxivity 2331 E. Outerand Second-Sphere Relaxivity 2334 F. Methods of Improving Relaxivity 2336 V. Macromolecular Conjugates 2336 A. Introduction 2336 B. General Conjugation Methods 2336 C. Synthetic Linear Polymers 2336 D. Synthetic Dendrimer-Based Agents 2338 E. Naturally Occurring Polymers (Proteins, Polysaccharides, and Nucleic Acids) 2339

https://mriquestions.com/uploads/3/4/5/7/34572113/lauffer_1999_review.pdf

Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications

Zircon is the main mineral in the majority of igneous and metamorphic rocks with Zr as an essential structural constituent. It is a host for significant fractions of the whole-rock abundance of U, Th, Hf, and the REE (Sawka 1988, Bea 1996, O’Hara et al. 2001). These elements are important geochemically as process indicators or parent isotopes for age determination. The importance of zircon in crustal evolution studies is underscored by its predominant use in U-Th-Pb geochronology and investigations of the temporal evolution of both the crust and lithospheric mantle. In the past decade an increasing interest in the composition of zircon, trace-elements in particular, has been motivated by the effort to better constrain in situ microprobe-acquired isotopic ages. Electron-beam compositional imaging and isotope-ratio measurement by in situ beam techniques—and the micrometer-scale spatial resolution that is possible—has revealed in many cases that single zircon crystals contain a record of multiple geologic events. Such events can either be zircon-consuming, alteration, or zircon-forming and may be separated in time by millions or billions of years. In many cases, calculated zircon isotopic ages do not coincide with ages of geologic events determined from other minerals or from whole-rock analysis. To interpret the geologic validity and significance of multiple ages, and ages unsupported by independent analysis of other isotopic systems, has been the impetus for most past investigations of zircon composition. Some recent compositional investigations of zircon have not been directly related to geochronology, but to the ability of zircon to influence or record petrogenetic processes in igneous and metamorphic systems.

Sedimentary rocks may also contain a significant fraction of zircon. Although authigenic zircon has been reported (Saxena 1966, Baruah et al. 1995, Hower et al. 1999), it appears to be very rare and may in fact be related to …

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The Composition of Zircon and Igneous and Metamorphic Petrogenesis

BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Physics and Applications of Bismuth Ferrite

Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.

Why Are There so Few Magnetic Ferroelectrics

The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.

Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides

13 Refractive indices of minerals and inorganic compounds can be calculated from their chemical 14 compositions using the additivity rule for electronic polarizabilities and converting the sum of 15 polarizabilities α using the Anderson-Eggleton relationship 𝛼 with the 16 molar volume V m solved for the mean refractive index n D at 589.3 nm. Whereas the polarizability 17 of cations is a single parameter, the polarizability of anions is described by a 2-parameter term 18 𝛼 (cid:2879) = 𝛼 (cid:2879)(cid:3042) ∙ 10 (cid:2879)(cid:3015) (cid:3290) /(cid:3023) (cid:3276)(cid:3289)(cid:3117).(cid:3118)(cid:3116) H-bonded hydroxyls ( 𝛼 (cid:2879)(cid:3042) =1.73 Å 3 , N o =2.042 Å 3.6 ). In an effort to understand the lower 23 polarizability of the H-bonded hydroxyl ions, we have evaluated observed and calculated 24 polarizabilities, O–H, H∙∙∙∙O, O∙∙∙∙O distances, and O–H∙∙∙∙O angles in 10 minerals with non- 25 hydrogen-bonded hydroxyls (mean <O∙∙∙∙O> distance 3.143 Å, mean <H∙∙∙∙O> distance 2.352 Å), 26 in 7 minerals with H-bonded-hydroxyls (<O∙∙∙∙O> = 2.739 Å, <H∙∙∙∙O> = 1.856 Å), and in 10 27 minerals with very strongly H-bonded hydroxyls (<O∙∙∙∙O> = 2.531 Å, <H∙∙∙∙O> = 1.525 Å). On the basis of quantum chemical cluster calculations using atomic parameters of well determined 29 crystal structures of hydroxyl containing compounds, we found that calculated intrinsic polarizabilities of OH are correlated with the hydrogen bond lengths H∙∙∙∙O and O∙∙∙∙O between 31 donor and acceptor of the H-bond. This is demonstrated for LiOH, brucite (Mg(OH) 2 ), 32 portlandite (Ca(OH) 2 ), clinometaborite (β-HBO 2 ), sassolite (H 3 BO 3 ), archerite (KH 2 PO 4 ), 33 kalicinite (KHCO 3 ), metaborite (γ-HBO 2 ), and NaPO 2 (OH) 2 . Thus, we find that these summed intrinsic polarizabilities for OH-bonds which are involved in H-bonding are significantly lower than the corresponding summed intrinsic polarizabilities for OH-bonds not involved in H-bonding. We attribute the reduction in polarizability of hydroxyl ions in clinometaborite, sassolite, archerite, kalicinite and metaborite, and the compound NaPO 2 (OH) 2 to the presence of H-bonds and a reduction of Hirshfeld atomic charge on the oxygen atom.

R. D. Shannon

Papers

Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides

Empirical electronic polarizabilities in