Infrared signatures of the dynamic Jahn-Teller effect in fullerene-based materials

Temperature‐dependent vibrational spectra show the evolution of dynamical Jahn‐Teller states in A(2)C(60) and A(4)C(60) fulleride salts. Whereas at low temperature the external field of the cations determines the local symmetry, at high temperature the fullerene balls distort into a D(3d) or D(5d) symmetry, independent of the surrounding lattice. The average structure is preserved while the molecules show pseudorotation between possible potential minima

Distortions of C-60(4-) studied by infrared spectroscopy

The Jahn-Teller effect plays a crucial role in the explanation of the insulating character of A(4)C(60) (A = K, Rb, Cs). To detect possible phase transitions arising from the interplay between the molecular Jahn-Teller distortion and the distorting potential field of the counterions, we measured the mid-IR spectra of A(4)C(60) compounds in the temperature range 90 - 300 K and found significant spectral changes with temperature in all three compounds. We also compare these spectra to that of Na(4)C(60) in its room-temperature polymeric phase, where the distortion is more pronounced and evident from the structure

Distortion and orientation of fulleride ions in A(4)C(60)

A(4)C(60) compounds (A = K, Rb, Cs) are good candidates to exhibit the Mott-Jahn-Teller insulating state. We present near-IR and neutron scattering data to reflect molecular and crystal stucture changes with temperature. We show how the size of the cation affects the structural and electronic properties of these compounds

Jahn-Teller distortion in Cs4C60 studied by vibrational spectroscopy

We have measured the infrared spectra of Cs(4)C(60) in the temperature range 220 - 450 K. Two anomalies in the low-frequency modes at 270 K and 400 K point to changes in molecular or crystal structure. The most probable explanation is a rotator phase above 400 K and a fully ordered phase below 220 K; the intermediate structure is one where molecular Jahn-Teller distortions compete with crystal field effects

Metallicity in fullerides

Metallic salts formed from fullerenes became popular because of their superconducting properties with a relatively high transition temperature, and were initially regarded as conventional metals and superconductors. Recently, owing to improved synthetic methods and a renewed interest in the study of their physical properties, many of them were found to exhibit exotic metallic and superconducting phases. In this paper, we summarize earlier results on unconventional metallic fulleride phases as well as the newly discovered expanded fulleride superconductors. The proximity of the Mott transition, a typical solid-state effect, results in molecular crystals, where molecular spectroscopic methods prove very successful. We concentrate on infrared and optical spectroscopy which is very well suited to follow metallicity and phase transitions in this class of substances

Ordered low-temperature structure in K4C60 detected by infrared spectroscopy

Infrared spectra of a K4C60 single-phase thin film have been measured between room temperature and 20 K. At low temperatures, the two high-frequency T1u modes appear as triplets, indicating a static D2h crystal-field stabilized Jahn-Teller distortion of the (C60)4- anions. The T1u(4) mode changes into the known doublet above 250 K, a pattern which could have three origins: a dynamic Jahn-Teller effect, static disorder between "staggered" anions, or a phase transition from an orientationally-ordered phase to one where molecular motion is significant.Comment: 4 pages, 2 figures submitted to Phys. Rev.

Die Ruptur der Supraspinatussehne : Arbeiten auf oder über Schulterniveau ; Ergebnisse aus einer Fall-Kontroll-Studie

In der vorliegenden Arbeit wurde in einer Fall-Kontroll-Studie mit 483 Fällen und 300 Kontrollen das Risiko für die berufsbedingte Supraspinatussehnenruptur durch Arbeiten auf oder über Schulterniveau untersucht. Dabei ergab sich eine statistisch signifikante Risikoerhöhung durch das Arbeiten auf oder über Schulterniveau. Eine Dosis-Antwortbeziehung zeigte einen Zusammenhang der Ereignisse. Am stärksten war die Risikoerhöhung bei Patienten, die lebenslang kumulativ mindestens 3195 Stunden auf oder über Schulterniveau arbeiteten. Die adjustierte Odds Ratio dafür betrug 2,1 (CI 1,2-3,7), das Ergebnis ist statistisch signifikant. Neben dem beruflichen Arbeiten auf oder über Schulterniveau gibt es andere Faktoren, die die Entstehung einer Rotatorenmanschettenruptur begünstigen. Dabei sind Alter, Heben/Tragen von Lasten über 20 kg und Arbeiten mit handgeführten vibrierenden Werkzeugen zu nennen. Deshalb wurden die Daten hinsichtlich dieser Faktoren adjustiert. Auch einige Sportaktivitäten können das Risiko für die Rotatorenmanschettenruptur erhöhen. Deshalb wurden die Daten auch für Geräteturnen, Kugelstoßen, Speer- und Hammerwerfen, Ringen und Tennis adjustiert, und die sportliche Anstrengung wurde als Confounder behandelt. Die Ergebnisse stehen im Einklang mit Ergebnissen früherer Studien, die ebenfalls eine Risikoerhöhung für die Entstehung der Rotatorenmanschettenruptur durch Arbeiten auf oder über Schulterniveau zeigen. Eine genaue Dosis, die zu dieser Risikoerhöhung führt, wurde in der Literatur bisher nicht genannt. Die vorliegende Arbeit liefert die Evidenz für die Annahme eines erhöhten Risikos der Ruptur der Sehne des M. supraspinatus bei Arbeiten auf oder über Schulterniveau. Weiterhin besteht ein Potential für eine primäre Prävention, indem Arbeiten auf oder über Schulterniveau möglichst ganz vermieden wird. Daher sollte die Ruptur der Sehne des M. supraspinatus als eigene Berufskrankheit in die Liste der Berufskrankheiten aufgenommen und die Betroffenen bei kumulativem Arbeiten von mindestens 3200 Stunden auf oder über Schulterniveau entschädigt werden.With this dissertation at hand the risk of a rupture of the rotator cuff caused by working at or above shoulder height was examined in a case control study with 483 cases and 300 controls. Working at or above shoulder height causes a statistically significant higher risk for this rupture. A dose-response relationship has been shown indicating a causal linking of the events. The strongest risk elevation has been found with patients, who worked life-long cumulative at least 3,195 – 64,057 hours at or above shoulder height. Therefore, the adjusted odds ratio is 2.1 (1.2-3.7). This result is statistically significant. Besides the occupational exposure of the rotator cuff and while working at or above shoulder height, there are other factors, which favour the formation of a rotator cuff rupture. Thus, the factors age, carrying/lifting of loads above 20 kg and working with hand-leaded vibrating tools are to be mentioned. Therefore, the data has been adjusted for these factors. Some sports activities can also cause a higher risk for this rupture. Hence, the data was also adjusted to apparatus gymnastics, shotput, javelin, hammer throwing, wrestling and for tennis. The strain of the sports activities was treated as a confounding variable. The results are in accordance with results from former studies, which also described a higher risk for a rotator cuff rupture while working with the hands at or above shoulder height. An exact dose with respect to this higher risk is not mentioned in the literature yet. The study shows the evidence of the assumption of a higher risk for the rupture of the tendon of the m. supraspinatus while working at or above shoulder height. Therefore, the possibility of primary prevention by avoiding work at or above shoulder height is given. Furthermore, the rupture of the tendon of the m. supraspinatus should be listed in the register of occupational diseases and the workers should be indemnified, if they worked cumulative at least 3200 hours at or above shoulder height

Nanosegregation in Na2C60

There is continuous interest in the nature of alkali metal fullerides containing C(4)(60) and C(2)(60), because these compounds are believed to be nonmagnetic Mott–Jahn–Teller insulators. This idea could be verified in the case of A(4)C(60), but Na(2)C(60) is more controversial. By comparing the results of infrared spectroscopy and X-ray diffraction, we found that Na(2)C(60) is segregated into 3-10 nm large regions. The two main phases of the material are insulating C(60) and metallic Na(3)C(60). We found by neutron scattering that the diffusion of sodium ions becomes faster on heating. Above 470 K Na(2)C(60) is homogeneous and we show IR spectroscopic evidence of a Jahn–Teller distorted C(2)(60) anion