TY - JOUR
T1 - Eu valency and recoil-free fraction in EuCo2Si2-xGex
AU - Perscheid, B.
AU - Nowik, I.
AU - Wortmann, G.
AU - Schmiester, G.
AU - Kaindl, G.
AU - Felner, I.
PY - 1989/12
Y1 - 1989/12
N2 - The valency of Eu in EuCo2Si2-xGex with x=0, 0.5, 1.0, and 2 was determined by151Eu-Mössbauer, Eu-LIII X-ray absorption as well as magnetization studies in the temperature range from 4.1 to 650 K and at external pressures up to 66 kbar. Eu in EuCo2Si2 is found to be predominantly trivalent, while in EuCo2Ge2 it is divalent. In EuCo2Si2-xGex (0≦x≦2), two separate narrow Mössbauer absorption lines are observed, corresponding to stable divalent and trivalent Eu ions. In EuCo2Si1.5Ge0.5, the relative spectral areas of the Eu2+ and Eu3+ Mössbauer lines are found to be strongly temperature and pressure dependent. A decrease in temperature or an application of pressure leads to small changes in the positions of the two absorption lines and to a pronounced increase in the relative spectral area of the Eu2+ component. On the other hand, X-ray absorption near-edge structure (XANES) measurements at the LIII threshold of Eu reveal no change in the relative intensity of the Eu2+ and Eu3+ subspectra as a function of temperature. From these observations it is concluded that the recoil-free fractions of the Eu2+ and Eu3+ Mössbauer resonances in EuCo2Si1.5Ge0.5 depend in a substantially different way on temperature. With the Debye approximation, Debye temperatures of θD(Eu2+)=175 K and ΘD(Eu3+)=250 K are derived. These results clearly show that relative abundances of Eu2+ and Eu3+ ions may only be derived from Mössbauer linie intensities, if appropriate corrections for differences in recoil-free fraction are applied; this applies even to mixed-valent systems, where Eu ions with different valencies occupy crystallographically equivalent sites.
AB - The valency of Eu in EuCo2Si2-xGex with x=0, 0.5, 1.0, and 2 was determined by151Eu-Mössbauer, Eu-LIII X-ray absorption as well as magnetization studies in the temperature range from 4.1 to 650 K and at external pressures up to 66 kbar. Eu in EuCo2Si2 is found to be predominantly trivalent, while in EuCo2Ge2 it is divalent. In EuCo2Si2-xGex (0≦x≦2), two separate narrow Mössbauer absorption lines are observed, corresponding to stable divalent and trivalent Eu ions. In EuCo2Si1.5Ge0.5, the relative spectral areas of the Eu2+ and Eu3+ Mössbauer lines are found to be strongly temperature and pressure dependent. A decrease in temperature or an application of pressure leads to small changes in the positions of the two absorption lines and to a pronounced increase in the relative spectral area of the Eu2+ component. On the other hand, X-ray absorption near-edge structure (XANES) measurements at the LIII threshold of Eu reveal no change in the relative intensity of the Eu2+ and Eu3+ subspectra as a function of temperature. From these observations it is concluded that the recoil-free fractions of the Eu2+ and Eu3+ Mössbauer resonances in EuCo2Si1.5Ge0.5 depend in a substantially different way on temperature. With the Debye approximation, Debye temperatures of θD(Eu2+)=175 K and ΘD(Eu3+)=250 K are derived. These results clearly show that relative abundances of Eu2+ and Eu3+ ions may only be derived from Mössbauer linie intensities, if appropriate corrections for differences in recoil-free fraction are applied; this applies even to mixed-valent systems, where Eu ions with different valencies occupy crystallographically equivalent sites.
UR - http://www.scopus.com/inward/record.url?scp=33748847876&partnerID=8YFLogxK
U2 - 10.1007/BF01319380
DO - 10.1007/BF01319380
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AN - SCOPUS:33748847876
SN - 0722-3277
VL - 73
SP - 511
EP - 517
JO - European Physical Journal B
JF - European Physical Journal B
IS - 4
ER -