title: Anomalous isotopic effect on the lattice parameter of silicon.
abstract: The difference Delta(a)=a(30)-a(28) of the lattice parameter of 30Si and 28Si crystals is measured over a temperature range from 4.7 to 700 K. In disagreement with existing knowledge, the strongest isotopic effect is not detected at the lowest achieved temperature T=4.7 K. An anomalous behavior is observed: The relative difference |Delta(a)/a| attains its maximum value of 56.8(5) ppm at T=75(10) K. The anomalous behavior is attributed to the influence of phonon modes with negative Grüneisen parameters. At T=700 K the effect still amounts to 30% of the maximal value. The experimental data are consistent with an approach based on the density-functional perturbation theory.
authors.affiliation: Institut für Experimentalphysik, Universität Hamburg, D-22761 Hamburg, Germany.
authors.forename: H-C
authors.initials: HC
authors.lastname: Wille
authors.forename: Yu V
authors.initials: YV
authors.lastname: Shvyd'ko
authors.forename: E
authors.initials: E
authors.lastname: Gerdau
authors.forename: M
authors.initials: M
authors.lastname: Lerche
authors.forename: M
authors.initials: M
authors.lastname: Lucht
authors.forename: H D
authors.initials: HD
authors.lastname: Rüter
authors.forename: J
authors.initials: J
authors.lastname: Zegenhagen