Study of Dielectric Properties of Oxygen-Postannealed $\hbox{Cu}_{0.5} \hbox{Tl}_{0.5}\hbox{Ba}_{2}\hbox{Ca}_{2}(\hbox{Cu}_{3 \hbox{-} {y}}\hbox{M}_{y})\hbox{O}_{10\hbox{-}\delta}$ Superconductor

The superconducting properties [onset temperature (
Tc
^onset
) and zero-resistivity critical temperature
Tc
(
R
= 0) ] and the dielectric properties [dielectric constants (ε
r
^/
, ε
r
^//
), absolute dielectric loss | tan δ|, and ac conductivity (σ
_ac
)] of oxygen-postannealed Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
(Cu
_3-
y
M
y
)O
_10-δ
(M = Si, Ge, Sn;
y
= 0, 1) superconductor have been studied. The superconducting properties have been increased in all undoped and Si-, Ge-, and Sn-doped samples after oxygen postannealing. The negative capacitance (NC) has been also observed in all postannealed Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
(Cu
_3-y
M
_y
)O
_10-δ
samples. Capacitance
C
and conductance
G
of Ge-doped Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
(Cu
₂
Ge
₁
)O
_{10 - δ}
and Sn-doped Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
(Cu
₂
Sn
₁
) O
_10-δ
samples have been increased after oxygen postannealing. In contrary, the values of
C
and
G
have been decreased in both the undoped Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
Cu
₃
O
_10-δ
and Si-doped Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
(Cu
₂
Si
₁
)O
_10-δ
samples after oxygen postannealing. The variation of
C
and
G
depends upon the degree of polarizibility, which is associated with carrier's density. The carrier's density depends upon the oxygen content, which can be controlled by oxygen postannealing. The appreciable change in the dielectric properties of Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
(Cu
_3-y
M
_y
)O
_10-δ
samples is the indication of oxygen variation after oxygen postannealing. These studies also show that the dielectric response of Cu
_0.5
Tl
_0.5
Ba
₂
Ca
₂
(Cu
_3-y
M
_y
)O
_10-δ
samples is strongly temperature and frequency dependent.