B-site Octahedral Bridge and A-site Polyvalent Cu cations Related Electron Hopping in LiCuNb3O9-based Colossal Permittivity Materials

2021 ◽  
Author(s):  
Dandan Gao ◽  
Jiyang Xie ◽  
Jian Wang ◽  
Wanbiao Hu
Keyword(s):  
Transition Metal ◽  
Electron Hopping ◽  
Colossal Permittivity ◽  
A Site

It has been widely accepted that the localized electron hopping induces colossal permittivity in the bulk of transition-metal-based materials. However, the mechanism and the control of electron hopping process remain...

scholarly journals High-pressure synthesis and physical properties of A-site ordered perovskites

2014 ◽  
Vol 70 (a1) ◽  
pp. C755-C755
Author(s):  
Youwen Long
Keyword(s):  
High Pressure ◽  
Transition Metal ◽  
Physical Properties ◽  
Colossal Magnetoresistance ◽  
Research Work ◽  
Negative Thermal Expansion ◽  
Transition Metal Ions ◽  
High Pressure Synthesis ◽  
Pressure Synthesis ◽  
A Site

ABO3-type perovskite oxides exhibit a wide variety of interesting physical properties such as superconductivity, colossal magnetoresistance, multiferroic behavior etc. For a simple ABO3 perovskite, if three quarters of the A site is replaced by a transition metal A', then the so-called A-site ordered double perovskite with the chemical formula of AA'3B4O12 can form. Since both A' and B sites accommodate transition metal ions, in addition to conventional B-B interaction, the new A'-A' and/or A'-B interaction is possible to show up, giving rise to the presence of many novel physical properties. Here we will show our recent research work on the high-pressure synthesis of several A-site ordered perovskites as well as a series of interesting physical properties like temperature- and pressure-induced intermetallic charge transfer, negative thermal expansion, magnetoelectric coupling multiferroic and so on. [1-3]

Ternary Rare Earth Transition Metal Zinc Compounds RT2Zn20 with T = Fe, Ru, Co, Rh, and Ni

1997 ◽  
Vol 52 (9) ◽  
pp. 1023-1030 ◽  
Author(s):  
Tono Nasch ◽  
Wolfgang Jeitschko ◽  
Ute Ch. Rodewald
Keyword(s):  
Rare Earth ◽  
Transition Metal ◽  
Metal Atom ◽  
Transition Metal Atom ◽  
Hexagonal Prism ◽  
Rare Earth Atom ◽  
Zinc Compounds ◽  
A Site ◽  
Cold Pressed ◽  
Zinc Site

Forty eight new compounds RT2Zn20 were prepared by annealing cold-pressed pellets of the elemental components in an argon atmosphere. They crystallize with the cubic CeCr2Al20 type structure (Fd3̅̅m , Z = 8), which was refined from single-crystal diffractometer data of TbFeiZn20 (a = 1411.1(1) pm ), YRu2Zn20 (a = 1422.6(1) pm ), DyRu2Zn20 (a = 1422.1(1) pm), GdCo2Zn20 (a = 1406.0(1) pm ), DyRh2Zn20 (a = 1418.2(1) pm ), and TmNi2Zn20 (a= 1401.6(1) pm) to conventional residuals varying betw een R = 0.011 and R - 0.024. The com pounds have a tendency for tw inning, thus m im icking hexagonal sym metry, with the cubic [111] axis as the axis w ith the pseudohexagonal symmetry. M inor inconsistencies in the cell volum es of these com pounds indicate slight deviations from the ideal com position. N evertheless, the five atom ic sites of this structure w ere found to be fully occupied w ithin the error lim its w ith the exception of one zinc site of TmNi2Zn20. The coordination for the site of the rare earth atom s is a Frank-K asper polyhedron with coordination num ber (CN) 16. The transition metal atom s occupy a site w ith icosahedral zinc coordination (CN 12). Two of the three zinc sites are in pentagonal prism atic coordination of zinc atom s, capped by rare earth and/or transition metal atom s (CN 12), w hile the third zinc site has 12 zinc neighbors form ing a hexagonal prism , w hich is capped by tw o rare earth atom s (CN 14).

scholarly journals Crystal Chemistry and Physics of Perovskites with Small Cations at the A Site

2014 ◽  
Vol 70 (a1) ◽  
pp. C976-C976
Author(s):  
Alexei Belik ◽  
Wei Yi ◽  
Qifeng Liang ◽  
Yoshitaka Matsushita ◽  
Masahiko Tanaka ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Transition Metal ◽  
Transition Metals ◽  
Crystal Chemistry ◽  
Ground States ◽  
Transition Metal Doping ◽  
Multiferroic Properties ◽  
Structural Distortions ◽  
Structural And Magnetic Properties ◽  
A Site

Synthesis, crystal chemistry, and physics of perovskites with small cations at the A site are an emerging field in perovskite science. Properties of ABO3 perovskites with small cations at the A site (A = Sc and In; B = transition metals) will be reported. ScBO3 and InBO3 perovskites extend the corresponding families of perovskites with A = Y, La-Lu, and Bi and exhibit larger structural distortions. As a result of large distortions, they show, in many cases, distinct structural and magnetic properties. It is manifested in B-site-ordered monoclinic structures of ScMnO3 [Inorg. Chem. 52 (2013) 9692] and `InMnO3' [Angew. Chem.: Inter. Ed. 49 (2010) 7723]; an unusual superstructure of ScRhO3 and InRhO3 [Inorg. Chem. 52 (2013) 12005]; two magnetic transitions in ScCrO3 and InCrO3 with very close transition temperatures [Chem. Mater. 24 (2012) 2197]; and antiferromagnetic ground states and multiferroic properties of Sc2NiMnO6 and In2NiMnO6 [Inorg. Chem. 52 (2013) 14108]. Features of such perovskites, such as, transition metal doping into the A site, (Sc1-xBx)BO3, will be discussed. Special attention will be given to new spin-driven multiferroics Sc2NiMnO6 and In2NiMnO6.

Evolution of transition metal charge states in correlation with the structural and magnetic properties in disordered double perovskites Ca2−xLaxFeRuO6 (0.5 ≤ x ≤ 2)

2021 ◽  
Vol 23 (38) ◽  
pp. 21769-21783
Author(s):  
Kumari Naveen ◽  
Tanmay Rom ◽  
Shams Sohel Islam ◽  
Manfred Reehuis ◽  
Peter Adler ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Transition Metal ◽  
Double Perovskites ◽  
Metal Charge ◽  
Electronic And Magnetic Properties ◽  
Structural And Magnetic Properties ◽  
Charge States ◽  
A Site

La-based B-site disordered double perovskites, Ca2−xLaxFeRuO6, have been investigated thoroughly. The effects of A-site substitution on the charge states and electronic and magnetic properties have been determined in a series of 3d/4d perovskites.

Electron spin resonance in natural kaolinites containing Fe3+ and other transition metal ions

Clay Minerals ◽  
1975 ◽  
Vol 10 (5) ◽  
pp. 313-345 ◽  
Author(s):  
R. E. Meads ◽  
P. J. Malden
Keyword(s):  
Electron Spin Resonance ◽  
Transition Metal ◽  
Metal Ions ◽  
Electron Spin ◽  
Transition Metal Ions ◽  
Crystal Fields ◽  
Hole Trapping ◽  
Spin Resonance ◽  
Crystal Field Parameters ◽  
A Site

AbstractA number of natural kaolinites from a variety of world sources have been investigated using electron spin resonance at both X-band and Q-band. The results show systematic differences some of which are related to the crystallinity of the material, some to the presence of transition metal ions other than Fe3+ and hole-trapping defects.The results provide evidence for at least three sites for substitution of Fe3+ having large crystal fields : (i) a site with near maximum rhombic character having crystal field parameters D > 1·2, λ = ⅓ the occurrence of which is correlated with lack of crystalline perfection due to stacking defects or to the proximity of surfaces, (ii) a site with less rhombic character with λ = 0·234, D = 0·585 as likely parameters, and (iii) a site with parameters near the values λ = 0·207, D = 0·322.Mössbauer and ESR evidence suggests that the principal sites of Fe3+ substitution are octahedral. The presence of Fe3+ in adjacent cation sites leads to a very broad resonance centred near geff = 2. Other resonances in the spectra are attributed to the effect of trapped holes, some at least of which are situated at oxygen sites adjacent to Al3+ ions substituting in sites normally occupied by Si4+.Hyperfine effects due to the presence of the transition ions Mn2+ and (VO)2+ are also observed.

ELECTRICAL AND MAGNETIC BEHAVIOR OF TRANSITION METAL OXIDES Ln0.7A0.3TMO3, Ln= La, Pr; A = Ca, Sr AND TM = Mn, Co

2010 ◽  
Vol 24 (06n07) ◽  
pp. 762-769 ◽  
Author(s):  
I. G. DEAC ◽  
A. VLĂDESCU ◽  
I. BALASZ ◽  
A. TUNYAGI ◽  
R. TETEAN
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Electrical Resistance ◽  
Low Temperatures ◽  
Ac Susceptibility ◽  
Magnetic Behavior ◽  
Boundary Effects ◽  
Spin Disorder ◽  
A Site

We present a detailed magnetic study of the polycrystalline transition metal oxides Ln 0.7 A 0.3 TMO 3, Ln = La , Pr ; A = Ca , Sr and TM = Mn , Co at low temperatures including electrical resistance, magnetization and ac susceptibility measurements. The effect of the A-site and B-site substitutions on the properties of these compounds is discussed. The results of this analysis indicate that the electrical and magnetic behavior of these compounds have some reminiscences of the manganites having similar formula, but the spin disorder and the grain boundary effects control the properties of these materials.

scholarly journals A Site-Selective Amination Catalyst Discriminates Between Nearly Identical C-H Bonds of Unsymmetrical Disubstituted Alkenes

2019 ◽  
Author(s):  
Tomislav Rovis ◽  
Honghui Lei
Keyword(s):  
Transition Metal ◽  
Transition Metal Complexes ◽  
Coupling Constants ◽  
Activation Barriers ◽  
Amination Reaction ◽  
The Difference ◽  
A Site ◽  
Synthetic Approaches ◽  
Site Selective ◽  
Synergistic Combinations

C−H activation reactions enable chemists to unveil new retrosynthetic disconnections and streamline conventional synthetic approaches. A longstanding challenge in C−H activation is the inability to distinguish electronically and sterically similar C–H bonds. Although numerous synergistic combinations of transition-metal complexes and chelating directing groups have been utilized to distinguish C−H bonds, undirected regioselective C−H functionalization strategies remain elusive. Herein, we report a regioselective C−H activation/amination reaction of various unsymmetrical dialkyl-substituted alkenes. The regioselectivity of C−H activation is correlated to the electronic properties of allylic C−H bonds indicated by the corresponding 1JCH coupling constants. A linear relationship between the difference of 1JCH coupling constants of the two competing allylic C−H bonds (Δ 1JCH) and the C−H activation barriers (Δ ΔG ‡ ) has also been determined.

Electron Hopping of Tris (2,2′-bipyridyl) Transition Metal Complexes M(bpy)2/33in Nafion

2016 ◽  
Vol 163 (7) ◽  
pp. H588-H597 ◽  
Author(s):  
Wayne L. Gellett ◽  
Krysti L. Knoche ◽  
Nadeesha P. W. Rathuwadu ◽  
Johna Leddy
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Electron Hopping
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