釔鋇銅氧化合物與二鋁化鈰奈米微粒之物性探討

The Physical Properties in YBa2Cu3O7-δ and CeAl2 Nanoparticles

洪慈蓮(Tsu-Lien Hung)

指導教授 ： 吳茂昆

國立清華大學/理學院/物理學系/碩士(2008年)

https://doi.org/10.6843/NTHU.2008.00520

摘要

溫度及壓力變化為探討物性的兩個重要的變因，本研究主要探討壓力與物性變化的關係，首先發展高壓比熱系統，主要利用鑽石高壓砧(Diamond anvil cell)結合熱弛豫法(Thermal relaxation method)，其優點為可量測樣品重量約5~10mg。本研究量測CeAl2在不同壓力下，其反鐵磁轉變溫度(TN)與壓力的關係，發現當壓力增加至4 kbar時，其TN從3.8 K增加至4.6 K。由於外加壓力使晶格產生些許變化，造成交換能改變而影響TN的變化。
將YBCO塊材製作成奈米微粒，使表面積效應造成樣品本身產生內壓力，造成晶格縮收達到加壓的效果。本研究利用準分子雷射濺鍍法製作奈米微粒，探討在零維的奈米尺度下，超導性質的改變。本實驗得到3 nm、35 nm及70 nm不同大小的YBCO奈米微粒，發現其超導轉變溫度皆在91 K，但70 nm樣品的超導成分比例只剩1.5%，且隨著尺寸的縮小，超導比例也跟著減少，至5 nm時，超導比例只剩下0.25%。Hc1也是隨著尺寸縮小而減少，從70 nm的HC1 為450 Oe到5 nm的HC1 為170 Oe。YBCO相干長度大約為2 nm，在粒徑5 nm時仍大於相干長度2 nm，故還有少部份的超導存在。

關鍵字

釔鋇銅氧化合物 ； 奈米微粒 ； 二鋁化鈰 ； 高壓

並列摘要

In this thesis our main objectives are to study the correlation between pressure and physical properties of materials that show interesting behavior. Temperature and pressure are two variables we used in this study as they are important parameters to better understand material characteristics. A major accomplishment in this study is the development of a high pressure specific heat system that utilizes a Diamond anvil cell together with the thermal relaxation method so that we can study small sample in the order of milligram. Using this high pressure specific heat system, we observed that the Neel temperature of CeAl2 increases with increasing pressure.
It is known nanoparticle can generate relatively large internal strain due to the surface effect and may change its physical properties. It is thus interesting to find out how the YBCO superconductor behaves if it is in nanoparticle form. We have fabricated with nanoparticle YBCO using pulsed laser deposition method. We found that for YBCO nanoparticles of sizes: 5nm, 35nm, and 70nm, their superconducting transition temperature remain to be ~ 90 K, however, the superconducting volume fraction is much reduced. For 70nm particle the volume fraction is ~ 1.5%, and for 5 nm only 0.25%. The critical field Hcl also decreases with size from 450 Oe for 70 nm particle down to 170 Oe for 5 nm.

並列關鍵字

YBCO nanoparticles ； CeAl2 ； high pressure ； specific heat

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