$r_{0}$. It is notable that $r_{0}$ increases for increasing $\beta $ (decreasing $\alpha $). In addition, we find that, for small values of $\alpha $ ($\alpha <\alpha _{c}$), there are two $r_{a}$ and $r_{b}$ ($r_{a}<r_{b}$), in which the black holes are stable for $%
r_{0}<r_{+}<r_{a}$ and $r_{+}>r_{b}$ (see Fig. \[CH1\] and also following three tables). Moreover, for large values of $\alpha $ ($\alpha >\alpha _{c}$) and $r_{+}>r_{c}$ the black holes are stable. We should note that for canonical ensemble one finds $r_{c}=r_{0}$ and for grand canonical ensemble $%
r_{c}>r_{0}$ (see Fig. \[CH2\]). Figs. \[CH3\] and \[CH4\] confirm that, regardless of value of $\beta $, we encounter an unstable phase for $%
\alpha <\alpha _{c}$.

  --------------------------------------------------------------------
    $r_{+}=$     $0.5$      $1$        $4$              $400$
  ---------- -- -------- --------- ------------ ----------------------
    $C_{Q}=$     $0.35$   $-2.9$      $5148$     $1.2\times 10^{13}$

        $H=$     $0.02$   $-0.03$   $4.8\times   $1.2\times 10^{-20}$
                                     10^{-5}$   
  --------------------------------------------------------------------

\
Table (1): corresponding to Fig. \[CH1\] for $\beta=0.05$.

  --------------------------------------------------------------------
    $r_{+}=$     $0.6$      $1$        $4$              $400$
  ---------- -- -------- --------- ------------ ----------------------
    $C_{Q}=$     $0.07$   $-4.8$      $5148$     $1.2\times 10^{13}$

        $H=$     $0.51$   $-0.13$   $4.8\times   $1.2\times 10^{-20}$
                                     10^{-5}$   
  --------------------------------------------------------------------

\
Table (2): corresponding to Fig. \[CH1\] for $\beta=0.5$.

  --------------------------------------------------------------------
    $r_{+}=$     $0.6$      $1$        $4$              $400$
  ---------- -- -------- --------- ------------ ----------------------
    $C_{Q}=$     $0.02$   $-9.25$     $5148$     