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Microstructure, magnetization and dc transport properties of MTG-YBa [iopmath latex="$_{1.8}$"] _{1.8} [/iopmath] Na [iopmath latex="$_{0.2}$"] _{0.2} [/iopmath] Cu_{3}O [iopmath latex="$_y$"] _{y} [/iopmath] crystal

### Abstract:

The Na-doping MTG-YBCO crystal with the nominal composition YBa [iopmath latex="$_{1.8}$"]_{1.8}[/iopmath] Na [iopmath latex="$_{0.2}$"]

_{0.2}[/iopmath] Cu

_{3}O [iopmath latex="$_y +40$"]

_{y}+ 40 [/iopmath] mol% Y211 has been successfully synthesized by the melted-textured-growth (MTG) method with top seed. The microstructure photographs show that the crystal has a good layered structure with a number of twins. There is a second peak in the magnetization curve for the magnetic field parallel to the

*c*-axis and at 77 K. The field of zero resistance temperature [iopmath latex="$T_{c0}$"]

*T*

_{c0}[/iopmath] shows a power law, [iopmath latex="$H=H_0$"]

*H*=

*H*

_{0}[/iopmath] ( [iopmath latex="$T_{c0}(0)-T_{c0}(H))^n$"]

*T*

_{c0}(0)-

*T*

_{c0}(

*H*))

^{n}[/iopmath] with [iopmath latex="$n=1.52$"]

*n*= 1.52 [/iopmath] for [iopmath latex="$H\parallel ab$"]

*H*

*ab*[/iopmath] and [iopmath latex="$n=1.41$"]

*n*= 1.41 [/iopmath] for [iopmath latex="$H\parallel c$"]

*H*

*c*[/iopmath] , respectively. The thermally activated flux creep model can scale the dissipative resistivity below the peak temperature [iopmath latex="$T_p$"]

*T*

_{p}[/iopmath] . The temperature and field dependences of the effective activation energy can be described by the formula [iopmath latex="$U=U_0(1-T/T_p)^mH^{-\alpha }$"]

*U*=

*U*

_{0}(1-

*T*/

*T*

_{p})

^{m}

*H*

^{-}[/iopmath] , where [iopmath latex="$m=1.75$"]

*m*= 1.75 [/iopmath] , [iopmath latex="$\alpha =0.75$"] = 0.75 [/iopmath] for [iopmath latex="$H\parallel ab$"]

*H*

*ab*[/iopmath] and [iopmath latex="$m=2.5$"]

*m*= 2.5 [/iopmath] , [iopmath latex="$\alpha =1.52$"] = 1.52 [/iopmath] for [iopmath latex="$H\parallel c$"]

*H*

*c*[/iopmath] , respectively. The effect of Na-doping induced disorder on flux pinning has been discussed.

**Document Type:** Miscellaneous

**Affiliations:**
**1: **
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China
**2: **
Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai 200050, People's Republic of China
**3: **
High Magnetic Field Laboratory, Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 23031, People's Republic of China

Publication date: January 1, 2001