Evidence for 4f-instability of dilute terbium in thorium

Abstract

We have measured the specific heat of dilute Th1−xTbx alloys (0.44 < x < 2.15 a/o), which rises linearly between 0.4 and 0.9 K with a slope of ΔC/T ≈ 450 mJ/K2molTb followed by a Schottky anomaly with a maximum near 3.8 K. The high temperature ΔχT product was found to be 4% lower than that of Tb3+. The resistivity shows no minimum at low temperatures. Discussion is made in terms of non-integral valence of Tb.