Cu掺杂对Sr_(3)YCo_(4-x)Cu_(x)O_(10.5+δ)多晶的结构与物理性能的影响

Effect of Cu Doping on the Structure and Physical Properties of Ordered Sr_(3)YCo_(4-x)Cu_(x)O_(10.5+δ)Polycrystals

采用固相反应法制备了Sr_(3)YCo_(4-x)Cu_(x)O_(10.5+δ)(x=0~1.0)系列多晶。利用热重-差示扫描量热分析、X射线衍射等表征了多晶的有序化相变,以及Cu掺杂对结构、热电输运性能和磁性能的影响。在固溶范围内(x=0~0.4),观察到XRD的有序峰(103)和(215),说明四方Sr_(3)YCo_(4-x)Cu_(x)O_(10.5+δ)多晶为超结构,这与合成时1000℃以上的吸氧(δ)放热相变有关;当x=0.6~1.0时,978℃在晶界处形成了单斜杂相。当x=0~0.4时,多晶呈半导体输运行为。随着Cu掺杂量的增加,空穴载流子浓度和迁移率增大,电阻率明显下降;此外,Co^(3+)离子自旋态降低,自旋熵增大,载流子浓度和自旋熵的共同作用使x=0~0.2多晶的热电势不变,x=0.4的热电势降低。磁化强度和铁磁转变温度(T_(c))降低,磁结构由G-型反铁磁转变为铁磁。在进行二次烧结后,300 K时电阻率明显降低,热电势为一次烧结的2倍,认为二次烧结提高结晶程度及铁磁有序排列。

Tetragonal Sr_(3)YCo_(4-x)Cu_(x)O_(10.5+δ)(x=0-1.0)polycrystals were prepared via solid-state reaction method.The ordered phase transformation and effect of Cu doping on structure,thermoelectric transport properties and magnetic properties were systematically studied by thermogravimetric-differential scanning calorimetry(TG-DSC),X-ray diffraction(XRD)et al.In the range of solid solubility(x=0-0.4),ordered peaks(103)and(215)are observed,indicating that tetragonal Sr_(3)YCo_(4-x)Cu_(x)O_(10.5+δ)polycrystals are superstructure,which is related to the ordering transformation of oxygen absorption(δ)with exothermic occurring above 1000℃in synthesis.When x=0.6-1.0,monoclinic phase form at the grain boundary(978℃),which destroys the order of Sr_(3)YCo_(4-x)Cu_(x)O_(10.5+δ)polycrystal.When x=0-0.4,polycrystals are semiconductor transport characterization.With the increase of Cu doping,hole carriers concentration and mobility improve,resistivity decreases obviously.And Co^(3+) spin-state decreases and spin entropy increases,the cooperation of carrier concentration and spin entropy make thermopower for x=0-0.2 polycrystals unchanged and decreases for x=0.4.Magnetization and ferromagnetic transition temperature(T_(c))decrease,magnetic structure transforms from G-type antiferromagnetic to ferromagnetic.After double sinter,resistivity decreases obviously at 300 K and thermopower is twice more than that of single sinter,indicating that the crystalline of polycrystal and improve ferromagnetic ordered alignment increase after double sinter.