Quasi-Skutterudite化合物中結構相變化之X光散射研究

Study of the Phase Transition in Quasi-Skutterudite Compounds Using X-ray Scattering

梁喻惠(Yu-Hui Liang)

指導教授 ： 杜昭宏

淡江大學/理學院/物理學系碩士班/碩士(2017年)

https://doi.org/10.6846/TKU.2017.00253

摘要

本論文利用X光散射與變溫實驗方法來研究Quasi-Skutterudite化合物中Sr3Ir4Sn13與Sr3Rh4Sn13調製結構相變化機制，其超導溫度TC分別為5K與4.2K，從電阻率量測上發現樣品分別於T*~147K與133K有相變化，認為由電荷密度波所致，伴隨結構相變化，於低溫時為體心立方結構，溫度高於T*，轉變為簡單立方結構。為探討於T*時的相變化原因，利用高解析度X光散射實驗，發現於低溫時產生一調製結構，此調製結構波方向為 ，為a×b平面結構，針對此調致結構進行變溫量測，觀察到其結構相變化為二階變化，相變溫度約146K。針對參雜了Ca的(Sr0.5Ca0.5)3Ir4Sn13 與Ca3Ir4Sn13進行變溫量測，其相變溫度降至76K與37K，推測由原子大小所導致的化學壓力使相變溫度下降。我們也針對布拉格繞射(4 4 0)進行變溫量測，觀察到於T*有非線性的變化，確認於T*有晶格結構相變化。

關鍵字

Quasi-Skutterudite化合物 ； 結構相變化 ； X光散射

並列摘要

The quasi-skutterudite Sr3Ir4Sn13 (SIS), and Sr3Rh4Sn13 (SRS) are superconductors with a transition temperature TC ~ 5 K (for SIS) and 4.2K (for SRS), respectively. Both materials also undergo an anomaly conductivity transition at T* ~ 147 K (SIS), and 133K (SRS), that is reported to be due to the formation of a charge-density wave (CDW). In order to confirm the existence of the CDW modulation, a high-resolution X-ray scattering experiment was conducted. Using high-resolution X-ray scattering on the beamline BL07, in the case of SIS, a modulated structure was observed to double the host lattice in a×b plane. The temperature dependence of the modulated reflection shows a second order phase transition with a transition temperature of about 146 K. Attempt was also played to study the doping effect on the CDW state, and we found that the temperature of phase transition for (Sr0.5Ca0.5)3Ir4Sn13 was down to ~ 76K. It suggests that the internal chemical pressure affects the transition temperature of CDW phase. Measurements on the Bragg reflection (4 4 0) in Sr3Ir4Sn13 and Sr3Rh4Sn13, also show a change in the size of the host lattice at about 146 K and 133K, suggesting that the anomaly at T*~ 147 K may be resulted from the lattice distortion.

並列關鍵字

Quasi-Skutterudite Compound ； X-ray Scattering ； Phase Transition

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