  The improvement of the quality factor Q0 of superconducting radio-frequency
(SRF) cavities at medium accelerating gradients (20-25 MV/m) is important in
order to reduce the cryogenic losses in continuous wave (CW) accelerators used
for a variety of applications. In recent years, SRF cavities fabricated from
ingot niobium have become a viable alternative to standard high-purity
fine-grain Nb for the fabrication of high-performing SRF cavities with the
possibility of significant cost reduction. Recent studies demonstrated the
improvement of Q0 at medium field in cavities heat treated at 800-1200 {\deg}C
without subsequent chemical etching [ ]. To further explore this treatment
procedure, a new induction furnace with an all-niobium hot-zone was
commissioned [ ]. A single-cell 1.5 GHz cavity fabricated from ingot material
from CBMM, Brazil, with RRR 200, was heat treated in the new furnace in the
temperature range 800-1400 {\deg}C for several hours. Residual resistance value
of 1 - 5 n\Omega have been consistently achieved on this cavity Q0-values as
high as 4.6\times1010 at 90 mT peak surface magnetic field at 2 K. Q0 values of
about ~2\times1011 have been measured at 1.5 K.
