以X光吸收光譜研究Si與Bi摻雜對CaMnO3電子結構之影響

Effects of Si and Bi Dopings on the Electronic Structure of CaMnO3 Studied by X-ray Absorption Spectroscopy

廖凡偉(Fan-Wei Liao)

指導教授 ： 張經霖

淡江大學/理學院/物理學系碩士班/碩士(2012年)

https://doi.org/10.6846/TKU.2012.00305

摘要

此論文是利用X光吸收光譜研究以Si及Bi分別摻雜 Mn與Ca之CaMnO3熱電材料之電子結構。在Si摻雜Mn的系列(CaMn1-xSixO3)中，由Mn L2，3-edge光譜發現Si部分取代Mn後，造成Mn4+組態濃度增加，x= 0.02時Mn4+ : Mn3+相對濃度變大，降低了電阻率。由Ca L2,3-edge及Mn L2,3-edge發現，Ca 3d與Mn 3d的未佔據態均減少，由O K-edge發現，當Si摻雜量為0.02時Mn 3d-O 2p未佔據態增加，原因可能為因Si的取代，導致Mn – O混成程度增加，因為Si引進了多餘的正電荷，所以增加了導電層(MnO2層)電子濃度因而降低了電阻率。
在摻雜Bi取代Ca系列(Ca1-xBixMnO3)中，由Mn L2，3-edge發現摻雜Bi取代Ca後，隨摻雜量增加， Mn4+ : Mn3+相對濃度有序的變大，使電阻率亦隨摻雜量變多而有序降低。由Ca L2,3-edge及Mn L2,3-edge發現，Ca 3d與Mn 3d的未佔據態均減少，由O K-edge發現，當摻雜增加，Mn 3d-O 2p未佔據態均增加，其原因可能為用較小的Bi與取代了較大的Ca，兩元素之間半徑雖然具有9%的差異，但由於此取代是作用於上下兩個MnO2層之間，因此拉近了MnO2層之間的距離使Mn-O混成程度增高，增加了導電層(MnO2層)電子濃度因而降低了電阻率。 在兩個系統中， Mn的平均價數均為+3.78價。

關鍵字

X光吸收光譜

並列摘要

We have performed x-ray absorption spectroscopy on two series of doped CaMnO3 in order to study the effect of electronic structure on the thermoelectric properties. In the CaMn1-xSixO3 series an electron transfer from Mn 4p to Mn 3d is observed, which enriches the charge carriers concentration in the MnO2 planes. We also found that the configuration concentration of Mn4+ is increasing. The increased carrierconcentration may be responsible for the increase conductivity in the Si-doped sample. In the Ca1-xBixMnO3 series a similar trend in the electronic structure due to the doping is observed. By comparing the effect of the doping dosage from 2% to 5%, we have determined that the variations of the electronic structure in these two series of samples are due to different mechanism. The average valence of Mn in the compounds CaMn1-xSixO3 and Ca1-xBixMnO3 are about 3.78 +.

並列關鍵字

XANES ； CaMnO3

參考文獻

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