Transport and structural study of ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CuO}}_{6+\mathrm{\delta }}$ single crystals prepared by the KCl flux method

${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{CuO}}_{6+\mathrm{\delta }}$ single crystals are prepared by a KCl flux method. Transport properties and crystal structures are investigated for the samples with various ${\mathit{T}}_{\mathit{c}}$’s. The result of structural analysis indicates that the change of ${\mathit{T}}_{\mathit{c}}$’s caused by the overdoping of the hole carrier through excess oxygen located between double Tl-O sheets. The out-of-plane resistivity ${\mathrm{\rho }}_{\mathit{c}}$ is larger than for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, but smaller than for ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$. Temperature dependences of ${\mathrm{\rho }}_{\mathit{c}}$ are metallic for both overdoped nonsuperconducting and 75-K superconducting samples. The temperature dependence of in-plane resistivity ${\mathrm{\rho }}_{\mathit{a}\mathit{b}}$ changes from ∼${\mathit{T}}^2$ to ∼${\mathit{T}}^1$ with increasing ${\mathit{T}}_{\mathit{c}}$. The Hall coefficient ${\mathit{R}}_{\mathit{H}}$ exhibits a characteristic maximum at about 100 K for all samples. However, inverse Hall mobility ${\mathrm{\mu }}_{\mathit{H}}^{\mathrm{-}1}$(=ρ/${\mathit{R}}_{\mathit{H}}$) always shows clear ${\mathit{T}}^2$ dependence regardless of the ${\mathit{T}}_{\mathit{c}}$ values, which suggests that the scattering rate of this material has ∼${\mathit{T}}^2$ dependence, just as in an ordinary Fermi liquid, and that the carrier concentration actually changes like that observed in ${\mathit{n}}_{\mathit{H}}$(=1/${\mathit{R}}_{\mathit{H}}$e).