Ca. Swenson, EXPANSIVITY AND HEAT-CAPACITY DATA FOR LU AND SC CRYSTALS FROM 1 TO 300 K - SPIN-FLUCTUATION AND ELECTRON-PHONON EFFECTS, Physical review. B, Condensed matter, 53(7), 1996, pp. 3669-3679
Linear thermal expansivity (alpha) measurements from 1 to 300 K and he
at capacity (C-p) measurements from 1 to 110 K are reported for single
crystals of the hexagonal scandium and lutetium metals; the C, data w
ere combined with previous data to obtain smooth representations to 30
5 K for Lu and 350 K for Sc. The Theta(0)'s (352 and 190 K, respective
ly, for Sc and Lu) and gamma's (10.38 and 8.30 mJ/mol K-2, respectivel
y for Sc and Lu) are in reasonable agreement with previous data of var
ious kinds. Electronic contributions are much larger for the alpha's t
han for the C-p's, with the large anisotropies of the alpha's primaril
y electronic in origin. The equivalent Debye Theta's for the lattice C
-p's and the Gruneisen parameters Gamma for the lattice alpha's both s
how an unexpected T dependence at ''high'' T (T greater than or simila
r to Theta(0)/2), which can be associated with the disappearance of sp
in-fluctuation and electron-phonon enhancements to the electronic prop
erties; this effect has been reported previously for Sc C-p's by Plesc
hiutschnig et al. [Phys. Rev. B 44, 6794 (1991)]. While the resulting
high-temperature ''bare'' or ''density of states'' gamma for Sc, gamma
(b)=5.75(25) mJ/mol K-2, is slightly larger than that calculated recen
tly by Gotz and Winter [J, Phys. Condens. Matter 5, 1721 (1993)], the
magnitude of the sum (gamma(spin)+gamma(ep)) agrees well. For Lu, for
which no recent calculations exist, gamma(b)=5.50(25) mJ/mol K-2. The
various Gamma's (a and c axis, lattice, and electronic) generally are
quite anisotropic, with no obvious correlation between high- and low-T
behavior. The anisotropy in Gamma which is associated with the enhanc
ement (spin plus e-p) contribution is very large, with similar magnitu
des for the c-axis values (similar to 17), but + for Lu and - for Sc.
A 186-at. ppm Fe impurity in the scandium crystals makes a significant
contribution to all of the data below 3.5 K. The resulting impurity G
amma's are very large and very anisotropic (Gamma(a)(Fe)=-40, Gamma(c)
(Fe)=30).