  The temperature and magnetic-field (H) dependences of thermal conductivity
(\kappa) of Bi_2Sr_2CaCu_2O_{8+\delta} (Bi2212) are systematically measured for
a broad doping range by using both pure Bi2212 single crystals with tuned
oxygen contents and Bi_2Sr_2Ca_{1-x}Dy_xCu_2O_{8+\delta} (Dy-Bi2212) single
crystals with different Dy contents x. In the underdoped samples, the
quasiparticle (QP) peak below T_c is strongly suppressed, indicating strong QP
scattering by impurities or oxygen defects, whereas the phonon conductivity is
enhanced in moderately Dy-doped samples and a phonon peak at 10 K is observed
for the first time in Bi2212 system, which means Dy^{3+} ions not only
introduce the impurities or point defects but also stabilize the crystal
lattice. The subkelvin data show that the QP heat conductivity gradually
decreases upon lowering the hole doping level. The magnetic-field dependence of
\kappa at temperature above 5 K is mainly due to the QP scattering off
vortices. While the underdoped pure Bi2212 show very weak field dependence of
\kappa, the Dy-doped samples present an additional "dip"-like term of \kappa(H)
at low field, which is discussed to be related to the phonon scattering by free
spins of Dy^{3+} ions. For non-superconducting Dy-Bi2212 samples with x \simeq
0.50, an interesting "plateau" feature shows up in the low-T \kappa(H)
isotherms with characteristic field at 1 -- 2 T, for which we discuss the
possible revlevance of magnon excitations.
