skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Combined effect of chemical pressure and valence electron concentration through the electron-deficient Li substitution on the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system

Abstract

Four members of the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system have been prepared by high-temperature reaction method and characterized by X-ray diffractions. All compounds crystallize in the orthorhombic Gd{sub 5}Si{sub 4}-type structure (space group Pnma, Pearson code oP16) with bonding interactions for interslab Ge{sub 2} dimers. The Li substitution for rare-earth elements in the RE{sub 4}LiGe{sub 4} system leads to a combined effect of the increased chemical pressure and the decreased valance electron concentration (VEC), which eventually results in the structure transformation from the Sm{sub 5}Ge{sub 4}-type with all broken interslab Ge–Ge bond for the parental RE{sub 5}Ge{sub 4} to the Gd{sub 5}Si{sub 4}-type structure for the ternary RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system. Site-preference between rare-earth metals and Li is proven to generate energetically the most favorable atomic arrangements according to coloring-problem, and the rationale is provided using both the size-factor and the electronic-factor related, respectively, to site-volume and electronegativity as well as QVAL values. Tight-binding, linear-muffin-tin-orbital (TB-LMTO) calculations are performed to investigate electronic densities of states (DOS) and crystal orbital Hamilton population (COHP) curves. The influence of reduced VEC for chemical bonding including the formation of interslab Ge{sub 2} dimers is alsomore » discussed. The magnetic property measurements prove that the non-magnetic Li substitution leads to the ferromagnetic (FM)-like ground state for Ce{sub 4}LiGe{sub 4} and the co-existence of antiferromagntic (AFM) and FM ground states for Sm{sub 4}LiGe{sub 4}. - Graphical abstract: Reported is a combined effect of the chemical pressure and the reduced VEC caused by the smaller monovalent non-magnetic Li substitution for the larger trivalent magnetic rare-earth metals in the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system. This results in the structure transformation from the Sm{sub 5}Ge{sub 4}-type to the Gd{sub 5}Si{sub 4}-type structure and the changes in magnetic properties. Display Omitted - Highlights: • Four Li-containing intermetallic compounds RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr and Sm) were synthesized. • The combined effect of the chemical pressure and the reduced VEC caused by Li substitution for a rare-earth metal results in the structure transformation. • Electronic structures and magnetic properties of title compounds were thoroughly investigated.« less

Authors:
; ;  [1];  [2];  [3];  [1]
  1. Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 361-763 (Korea, Republic of)
  2. Department of Chemistry, Chungnam National University, Daejeon, Chungnam 305-764 (Korea, Republic of)
  3. Advanced Materials Research Center, Samsung Advanced Institute of Technology, Yongin-si, Gyeonggi-do 446-712 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22274064
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 205; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CRYSTALS; DENSITY; ELECTRONEGATIVITY; GROUND STATES; INTERACTIONS; INTERMETALLIC COMPOUNDS; MAGNETIC PROPERTIES; ORTHORHOMBIC LATTICES; RARE EARTHS; SPACE GROUPS; TRANSFORMATIONS; X-RAY DIFFRACTION

Citation Formats

Nam, Gnu, Jeon, Jieun, Kim, Youngjo, Kwon Kang, Sung, Ahn, Kyunghan, and You, Tae-Soo, E-mail: tsyou@chungbuk.ac.kr. Combined effect of chemical pressure and valence electron concentration through the electron-deficient Li substitution on the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system. United States: N. p., 2013. Web. doi:10.1016/J.JSSC.2013.06.027.
Nam, Gnu, Jeon, Jieun, Kim, Youngjo, Kwon Kang, Sung, Ahn, Kyunghan, & You, Tae-Soo, E-mail: tsyou@chungbuk.ac.kr. Combined effect of chemical pressure and valence electron concentration through the electron-deficient Li substitution on the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system. United States. doi:10.1016/J.JSSC.2013.06.027.
Nam, Gnu, Jeon, Jieun, Kim, Youngjo, Kwon Kang, Sung, Ahn, Kyunghan, and You, Tae-Soo, E-mail: tsyou@chungbuk.ac.kr. 2013. "Combined effect of chemical pressure and valence electron concentration through the electron-deficient Li substitution on the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system". United States. doi:10.1016/J.JSSC.2013.06.027.
@article{osti_22274064,
title = {Combined effect of chemical pressure and valence electron concentration through the electron-deficient Li substitution on the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system},
author = {Nam, Gnu and Jeon, Jieun and Kim, Youngjo and Kwon Kang, Sung and Ahn, Kyunghan and You, Tae-Soo, E-mail: tsyou@chungbuk.ac.kr},
abstractNote = {Four members of the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system have been prepared by high-temperature reaction method and characterized by X-ray diffractions. All compounds crystallize in the orthorhombic Gd{sub 5}Si{sub 4}-type structure (space group Pnma, Pearson code oP16) with bonding interactions for interslab Ge{sub 2} dimers. The Li substitution for rare-earth elements in the RE{sub 4}LiGe{sub 4} system leads to a combined effect of the increased chemical pressure and the decreased valance electron concentration (VEC), which eventually results in the structure transformation from the Sm{sub 5}Ge{sub 4}-type with all broken interslab Ge–Ge bond for the parental RE{sub 5}Ge{sub 4} to the Gd{sub 5}Si{sub 4}-type structure for the ternary RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system. Site-preference between rare-earth metals and Li is proven to generate energetically the most favorable atomic arrangements according to coloring-problem, and the rationale is provided using both the size-factor and the electronic-factor related, respectively, to site-volume and electronegativity as well as QVAL values. Tight-binding, linear-muffin-tin-orbital (TB-LMTO) calculations are performed to investigate electronic densities of states (DOS) and crystal orbital Hamilton population (COHP) curves. The influence of reduced VEC for chemical bonding including the formation of interslab Ge{sub 2} dimers is also discussed. The magnetic property measurements prove that the non-magnetic Li substitution leads to the ferromagnetic (FM)-like ground state for Ce{sub 4}LiGe{sub 4} and the co-existence of antiferromagntic (AFM) and FM ground states for Sm{sub 4}LiGe{sub 4}. - Graphical abstract: Reported is a combined effect of the chemical pressure and the reduced VEC caused by the smaller monovalent non-magnetic Li substitution for the larger trivalent magnetic rare-earth metals in the RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr, and Sm) system. This results in the structure transformation from the Sm{sub 5}Ge{sub 4}-type to the Gd{sub 5}Si{sub 4}-type structure and the changes in magnetic properties. Display Omitted - Highlights: • Four Li-containing intermetallic compounds RE{sub 4}LiGe{sub 4} (RE=La, Ce, Pr and Sm) were synthesized. • The combined effect of the chemical pressure and the reduced VEC caused by Li substitution for a rare-earth metal results in the structure transformation. • Electronic structures and magnetic properties of title compounds were thoroughly investigated.},
doi = {10.1016/J.JSSC.2013.06.027},
journal = {Journal of Solid State Chemistry},
number = ,
volume = 205,
place = {United States},
year = 2013,
month = 9
}
  • We have studied the effect of the valence electron concentration, on the bulk modulus and the chemical bonding in Ta{sub 2}AC and Zr{sub 2}AC (A=Al, Si, and P) by means of ab initio calculations. Our equilibrium volume and the hexagonal ratio (c/a) agree well (within 2.7% and 1.2%, respectively) with previously published experimental data for Ta{sub 2}AlC. The bulk moduli of both Ta{sub 2}AC and Zr{sub 2}AC increase as Al is substituted with Si and P by 13.1% and 20.1%, respectively. This can be understood since the substitution is associated with an increased valence electron concentration, resulting in band fillingmore » and an extensive increase in cohesion.« less
  • Photoionization can generate a non-stationary electronic state, which leads to coupled electron-nuclear dynamics in molecules. In this article, we choose benzene cation as a prototype because vertical ionization of the neutral species leads to a Jahn-Teller degeneracy between ground and first excited states of the cation. Starting with equal populations of ground and first excited states, there is no electron dynamics in this case. However, if we add methyl substituents that break symmetry but do not radically alter the electronic structure, we see charge migration: oscillations in the spin density that we can correlate with particular localized electronic structures, withmore » a period depending on the gap between the states initially populated. We have also investigated the effect of nuclear motion on electron dynamics using a complete active space self-consistent field (CASSCF) implementation of the Ehrenfest method, most previous theoretical studies of electron dynamics having been carried out with fixed nuclei. In toluene cation for instance, simulations where the nuclei are allowed to move show significant differences in the electron dynamics after 3 fs, compared to simulations with fixed nuclei.« less
  • The crystal structure and the Yb valence of the YbFe 2Ge 2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. Furthermore, the measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr 2Si 2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from vmore » = 2.72(2) at ambient pressure to v = 2.93(3) at ~9 GPa, where at low temperature a pressure-induced quantum critical state was reported.« less
  • We measured the crystal structure and the Yb valence of the YbFe 2Ge 2 heavy fermion compound at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. Moreover, the measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. Finally, while the ThCr 2Si 2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence frommore » v = 2.72(2) at ambient pressure to v = 2.93(3) at ~9 GPa, where at low temperature a pressure-induced quantum critical state was reported.« less
  • We demonstrate that the action of physical pressure, chemical compression, or aliovalent substitution in ACo(2)As(2) (A = Eu and Ca) has a general consequence of causing these antiferromagnetic materials to become ferromagnets. In all cases, the mixed valence triggered at the electropositive A site results in the increase of the Co 3d density of states at the Fermi level. Remarkably, the dramatic alteration of magnetic behavior results from the very minor (<0.15 eleetron) change in the population of the 3d orbitals. The mixed valence state of En observed in the high-pressure (HP) form of EuCo2As2 exhibits a remarkable stability, achievingmore » the average oxidation state of +2.25 at 12.6 GPa. In the case of CaCo2As2, substituting even 10% of Eu or La into the Ca site causes ferromagnetic ordering of Co moments. Similar to HP-EuCo2As2, the itinerant 3d ferromagnetism emerges from electronic doping into the Co layer because of chemical compression of Eu sites in Ca0.9Eu0.1Co1.91As2 or direct electron doping in Ca0.85La0.15Co1.89As2. The results reported herein demonstrate the general possibility of amplifying minor localized electronic effects to achieve major changes in material's properties via involvement of strongly correlated electrons.« less