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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/80373

    Title: 助熔劑法合成鹼金屬碲酸鹽及其結構研究;Flux Synthesis and Characterization of Alkali Metal Tellurates
    Authors: 李柏驛;Lee, Po-Yi
    Contributors: 化學學系
    Keywords: 碲酸鹽;非線性光學;助熔劑法
    Date: 2019-07-17
    Issue Date: 2019-09-03 14:27:19 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 本研究以助熔劑法成功合成出三個新穎鹼金屬碲酸鹽氧化物NaTeO3(OH) (A1)、δ-Na2TeO4 (A2)及Na3Te5O14 (A3),三個化合物由單晶X光繞射實驗,鑑定出化合物的晶體結構,並透過 EDS 確定化合物元素組成沒有其它多餘元素參雜於化合物中,A1及A2外型為透明片狀與透明柱狀晶體皆為非中心對稱的一維鏈狀結構,兩化合物空間群同樣屬於Cmc21 ,兩者在結構中碲與氧的配位模式皆為三角柱狀與以往文獻中常報導的八面體結構有相當大的差異,這是首次在碲酸鹽氧化物結構中發現這種新型的配位模式,兩化合物透過TeO6 三角柱共用邊相連成一維無限延伸鏈狀結構,A3空間群為P1 ̅為三維網狀結構也是第一個在鈉碲酸鹽之中首個被發現的混價化合物顏色為紅棕色,結構中由八面體之[ TeO6 ]單元中的四個氧接上同樣為八面體之[ TeO6 ]單元,其餘兩個氧接上兩個四角錐之[ Te4+O5 ]以此模式向三個方向無限延伸,化合物A2透過理論計算得知其穩定性比β-Na2TeO4差,透過示差掃瞄熱分析儀得知化合物A2分解溫度為707°C然而β-Na2TeO4分解溫度為745°C,實驗和理論計算結果吻合,利用Kurtz–Perry方法於 1064 nm的雷射下分析粉末二次倍頻效率有0.3*SiO2,顯示出此碲酸鹽類晶體具有做為非線性光學材料的潛力。;Three new alkali tellurates, NaTeO3(OH) (A1), δ-Na2TeO4 (A2) and Na3Te5O14 (A3) , were synthesized by the flux method, and their crystal structures were determined by single crystal X-ray diffraction, and further characterized by EDS, DSC/TG, XPS, PSHG, and DFT calculation.
    A1 and A2 both one-dimensional infinity chain structure are formed of edge-sharing TeO6 trigonal prisms with the Na+ cations between the chains. This is the first compound that contains trigonal prismatic TeO6 only, whereas Te6+ is almost invariably octahedrally coordinated by oxygen. DSC/TG analysis shows that A2 undergoes a reversible solid state transition at 416 °C and melts with decomposition above 707 °C. A2 is the least stable polymorph as indicated by the results from thermal analysis and DFT calculations on the other polymorphs. The powder second harmonic generation (PSHG) test showed that it features a remarkable SHG effect of about 0.3 times of SiO2. A3 has a centrosymmetric three-dimensional framework structure containing 3- and 6-ring channels with the Na+ cations at the center of the channels. A3 also is the first mix valence compound. These three tellurates compounds are compared with those in the literature. A3 also is the first example of a mixed valence compound of anhydrous sodium oxotellurate. The flux reaction is a versatile method to synthesize new tellurate materials for NLO applications.
    Appears in Collections:[Graduate Institute of Chemistry] Electronic Thesis & Dissertation

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