鑭系鋯氧焦綠石結構系列晶體生長及物性分析

Crystal Growth and Characterization of Pyrochlore-related Lanthanide Zirconate

王冠仁(kuan-Jen Wang)

指導教授 ： 林鴻明 ； 吳茂昆

大同大學/工程學院/材料工程學系所/碩士(2010年)

摘要

鑭鋯氧燒綠石材料因為有豐富的化學性質、低熱傳導性質、高熱膨脹係數、和化學穩定性，一直以來被認為在各方面有廣泛的應用。例如核廢料回收、汽車廢氣淨化的催化、高溫熱脹塗層、螢光載體中心和氧化催化劑上。在本篇論文中，我們成功的使用懸浮熔區法生長了鑭系元素鋯氧單晶（鑭系元素包括鑭、釹、釓、钬、鉺），微觀方面，單晶的晶軸方向和品質藉由粉末和單晶Ｘ光繞射儀來鑑定，我們使用這些單晶來研究光學、硬度、熱傳導和介電等物理參數及性質。在主要的巨觀光學性質中，鑭鋯氧和釓鋯氧因為在可見光範圍中沒有吸收，顏色上呈現白色透明，釓鋯氧、钬鋯氧和鉺鋯氧有多重峰值的吸收，在不同光源下有不同的顏色。在晶體的硬度方面，晶粒大小對硬度都有很大的影響，硬度約為103 Mpa，和文獻的塊材相比約小十倍 [31]，因為晶粒越小硬度越大，所以可以間接證明晶體的品質。熱傳導方面，我們得到的鉺鋯晶體的本徵熱傳導數值比文獻的塊材數值還要高 [122]，我們也推測稀土元素的摻入引起的氧化鋯晶格和原子間作用力的變化對於本徵熱導率具有重要影響。介電常數方面，燒綠石結構的鑭鋯氧晶體的獨特的介電圖形，而其他瑩石結構的晶體有很大的不同，這則是由燒綠石結構而產生的離子躍遷和偶極鬆弛有關。

關鍵字

懸浮熔區 ； 晶體生長 ； 鑭鋯氧 ； 燒綠石

並列摘要

The Lanthanide zirconate pyrochlores (Ln2Zr2O7) with pyrochlore structure has complex chemistry, low thermal conductivity, high thermal expansion coefficient, and high chemical stability behaviors, which are considered to have wide applications, such as nuclear applications, sub-catalysts for automotive exhaust gases, high-temperature thermal-barrier-coating materials, hosts for fluorescence centers, and oxidation catalysts. In order to investigating those physical parameters and intrinsic properties, single crystal is the best approach to being with of. However, in actual experiments, Ln2Zr2O7 crystals is difficult to grow because of their extremely high melting points and hard to keep the right composition of oxide at high temperature (~3000 K). In this thesis, we present results of successful growth of single crystals of Ln2Zr2O7 (Ln = La, Nd, Gd, Ho, and Er) by floating-zone method. Crystal structure and quality were identified by powder and single crystal x-ray diffraction. In general appearance, the colors of the crystals depend on the wavelength of the exerted light source. Without absorptions in the visible light, La2Zr2O7 and Gd2Zr2O7 crystals are white and transparent. Multiple absorptions of Nd2Zr2O7, Ho2Zr2O7, and Er2Zr2O7 crystals result in different colors. It has been found that the smaller the grain size the greater the hardness. The hardness of these crystals is about 103 MPa and is 10 times lower than those in the literatures [31] and represents the quality of the crystals. In specify substituted elements in A site, thermal conductivity of Er2Zr2O7 crystal is higher than one of bulk samples from the literatures [122]. It revealed the intrinsic thermal conductivity which is related with the effect of rare earth elements on zirconia lattice distortion and interatomic action force. For dielectric constants, La2Zr2O7 crystal being pyrochlore structure shows different behavior from other fluorites. The special figure of dielectric constant comes from the pyrochlore structure and the energy loss of pyrochlore seems to be result of ion jumping and dipole relaxation.

並列關鍵字

crystal growth ； Lanthanide zirconate pyrochlore ； Pyrochlore ； floating zone

參考文獻

[102] 葉國偉,”鉍鍶鈣銅氧系列超導單晶晶體生長與晶體性質之研究”(2007) 國立清華大學博士班論文

[2] E. Aleshin, and R. Roy, J. Am. Ceram. Soc. 45 (1962) pp.18.

[3] A. Mergen, and W.E. Lee, Mater. Res. Bull. 32 2 (1997) pp.175.

[5] W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, “Introduction to Ceramics” (1991) pp.913.

[6] Ion Bunget, and Mihai Popescu, “Physics of Solid Dielectrics” (1984) pp.207.