947 resultados para Cr^3
Resumo:
CrAl2O3Al2O3Cr^3Mg^2Cr^4Cr^41223nmCr^437nm
Resumo:
-Ga2O3Cr-Ga2O3CrDqRacah10Dq/B=2314Cr^3-Ga2O3-Ga2O3CrCr^3420nm691nmCr^3^4T2^4A2
Resumo:
Fe/CrFe/CrCr(III)/Cr(VI)Cr(III)/Cr(rIII)Cr(III)/Cr(II)Pb~(2+)Cr(III)/Cr(II)PbInTlPb-InPb-TlPbTlPbInTl[Cr(H_2O)_4Cl_2] Cl2H_2O <-> [Cr(H_2O)_5Cl]Cl_2H_2O<->[Cr(H_2O)_6]Cl_3Cr(III)Cr(III)i_pCr(H_2O)_4Cl_2~+Cr(H_2O)_5Cl~+-550mvvsscE-660mvvsscECr(H_2O)_4Cl_2~+Cr(H_2O)_5Cl~2+Cr(H_2O)_5Cl~(2+)Cr(H_2O)_4Cl_2~+Cr~(3+)Cr~(3+)Cr(III)/Cr(II)20mA/cm~299601.18VCr(III)/Cr(VI)Cr(III)/Cr(II)PtCr(III)/Cr(VI)Cr(III)Pb~(2+), Co~(2+)Cr(III)Ag~+Cr(III)Ag~+Cr(III)Cr(III)0.1m_PlogV2_p/2logv=100mvi_pv0.07MPtCr(III)
Resumo:
Al(2)O(3):Eu(3+)(1%) samples were prepared by combustion, ceramic, and Pechini methods annealed from 400 to 1400 degrees C. XRD patterns indicate that samples heated up to 1000 degrees C present disordered character of activated alumina (gamma-Al(2)O(3)). However, alpha-Al(2)O(3) phase showed high crystallinity and thermostability at 1200-1400 degrees C. The sample characterizations were also carried out by means of infrared spectroscopy (IR), scanning electron microscopy (SEM) and specific surface areas analysis (BET method). Excitation spectra of Al(2)O(3):Eu(3+) samples present broaden bands attributed to defects of Al(2)O(3) matrices and to LMCT state of O -> Eu(3+), however, the narrow bands are assigned to (7)F(0) -> (5)D(J),(5)H(J) and (5)L(J) transitions of Eu(3+) ion. Emission spectra of samples calcined up to 1000 degrees C show broaden bands for (5)D(0) -> (7)F(J) transitions of Eu(3+) ion suggesting that the rare earth ion is in different symmetry sites showed by inhomogeneous line broadening of bands, confirming the predominance of the gamma-alumina phase. For all samples heated from 1200 to 1400 degrees C the spectra exhibit narrow (5)D(0) -> (7)F(J) transitions of Eu(3+) ion indicating the conversion of gamma to alpha-Al(2)O(3) phases, a high intensity narrow peak around 695 nm assigned to R lines of Cr(3+) ion is shown. Al(2)O(3):Eu(3+) heated up to 1100 degrees C presents an increase in the Omega(2) intensity parameter with the increase of temperatures enhancing the covalent character of metal-donor interaction. The disordered structural systems present the highest values of emission quantum efficiencies (eta). CIE coordinates of Al(2)O(3):Eu(3+) are also discussed. (C) 2007 Elsevier Inc. All rights reserved.
Resumo:
Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K2Cr8O16, which exhibits a temperature-dependent (T-dependent) paramagnetic-to-ferromagnetic- metal transition at T-C = 180 K and transforms into a ferromagnetic insulator below T-MI = 95 K. We observe clear T-dependent dynamic valence (charge) fluctuations from above T-C to T-MI, which effectively get pinned to an average nominal valence of Cr+3.75 (Cr4+:Cr3+ states in a 3:1 ratio) in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0) similar to 3.5(k(B)T(MI)) similar to 35 meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U similar to 4 eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr) and the half-metallic ferromagnetism in the t(2g) up-spin band favor a low-energy Peierls metal-insulator transition.
Resumo:
KMgF_3:Eu~(2+)KMgF_3:Eu~(2+)-X(X=Gd~(3+)Ce~(3+)Cr~(3+)Cu~(+))12UV-Vis300 K77 KEu~(2+)4Eu~(2+) ~6P_(7/2)Eu~(2+)Ce~(3+)d-dKMgF_3:Eu~(2+)
Resumo:
Cr-Al-OCr_2O_3/Al_2O_3Cr_2O_3/Al_2O_3 LaCePrNdCeSEMCr_2O_3/Al_2O_3VCr~(3+)V~(5+)O~(2-)Cr~(3+)V~(4+)O~-Cr~(2+)V~(5+)O~-O~-C_3~0C_3H_7OH~-TPDVTmO_2~-O~O~-O_2~-O_2~-C_3~-Mo-Al-OMoO_3/Al_2O_3C_3~0MoO_3/Al_2O_3VFe, XRDMoO_3/Al_2O_3MoO_3wt%MoO_3Al_2(MoO_4)_3
Resumo:
TPRDRSX-XRDESRMSXPSAESCo/Al_2O_3Mo/Al_2O_3CoMo/Al_2O_3K_2CO_3CoMoK/Al_2O_3Mg~(2+)Zn~(2+)Cu~(2+)Cr~(3+)Al_2O_3Co
Resumo:
KegginZW_(11)O_(39)M(H_2O)~(n-)(Z=Si,Ge,P;M=Ni~(2+),C~(2+),Cr~(3+),Co~(2+);n=46)DawsonP_2W_(17)O_(61)M(H_2O)~(n-)(M=Ni~(2+),Cu~(2+),Cr~(3+),Co~(2+);n=7,8)(),,.Lewis,,,,ESR.,,,,ZW_(11)O_(39)M(L)~(n-)+PyZW_(11)O_(39)M(Py)~(n-)+L(L=).,,.
Resumo:
(=1-kh),N,f_cd_L,h:h=(f_c_LN)~(1/2),hCr~(3+),Co~(2+),Ni~(2+),Mn~(2+),Ti~(2),V~(2+),Cr~(2+),Fe~(2+)k
Resumo:
ZrO_2-Y_2O_3(88:12mol%),~(60)Co (Y_(Zr),Vo)Cr~(3+)Er~(3+)3d~33Cr~(3+)BCD_q
Resumo:
PPbCuPbZnCdCr~(3+)Cr~(6+)NiCoMnFeAs~(3+)As~(5+)Se~(4+)Se~(6+)HgF-pH,,,0.45pH1.5(AsSe),Hg,(),4
Resumo:
1Fe~(2+)Ti~(4+)Fe~(2+)Fe~(3+)Fe~(3+)Cr~(3+)Fe~(2+)Fe~(3+)Ti~(3+)Ti~(4+)Cr~(3+)Mn~(2+)Fe~(2+)/Ti~(4+)Fe~(3+)/Fe~(2+)FeTi2345
Resumo:
Thiol-functionalized mesoporous ethane-silicas with large pore were synthesized by co-condensation of 1,2-bis(trimethoxy-sily)ethane (BTME) with 3-mercaptopropyltrimethoxysilane (MPTMS) using nonionic oligomeric polymer C1H (OCH(2)-CH(2))(10)OH (Brij-76) or poly(alkylene oxide) block copolymer (P123) as surfactant in acidic medium. The results of powder X-ray diffraction (XRD), nitrogen gas adsorption, and transmission electron microscopy (TEM) show that the resultant materials have well-ordered hexagonal mesoscopic structure with uniform pore size distributions. (29)Si MAS NNR, (13)C CP-MAS NMR. FT-IR, and UV Raman spectroscopies confirm the attachment of thiol functionalities in the mesoporous ethane-sificas. The maximum content of the attached thiol group (-SH) in the mesoporous framework is 2.48mmol/g. The ordered mesoporous materials are efficient Hg(2+) adsorbents with almost every -SH site accessible to Hg(2+). In the presence of various kinds of heavy metal ions such as Hg(2+), Cd(2+), Zn(2+), Cu(2+) and Cr(3+), the materials synthesized using poly(alkylene oxide) block cooollxmier (Pluronic 123) g(2+), as surfactant show almost similar affinity to Hg(2+), Cd(2+), and Cr(3+), while the materials synthesized using ofigomeric polymer C(18)H(37)(OCH(2)CH(2))(10)OH (Brij-76) as surfactant exhibit high selectivity to Hg(2+). (C) 2004 Elsevier Inc. All rights reserved.