王 志 國,向 俊 尤,萬 素 磊，武 柯 含，魯 毅,趙 建 軍

(包頭師范學(xué)院 物理科學(xué)與技術(shù)學(xué)院，內(nèi)蒙古 包頭 014030)

1 實(shí)驗(yàn)方法

將原料La2O3、Gd2O3、MnCO3和SrCO3通過固相反應(yīng)法合成(La0.9Gd0.1)4/3Sr5/3Mn2O7多晶樣品。實(shí)驗(yàn)中所用的氧化物純度都大于99.9%。充分混合研磨按比例稱量的各組分氧化物，將研磨后粉末在1000℃下預(yù)燒12h。然后再將預(yù)燒后的粉末研磨并在相同條件下進(jìn)行第二次預(yù)燒，最后，將兩次預(yù)燒后的粉末研磨、壓片。并將片狀樣品在1350℃煅燒24h并隨爐冷卻，最后，得到外觀平整、堅(jiān)硬而無裂痕的圓形塊狀樣品。用X射線衍射儀檢測樣品的單相性。樣品的磁化強(qiáng)度與溫度的關(guān)系(M-T曲線)和電阻與溫度的關(guān)系(R-T曲線)是通過美國Quantum Design公司設(shè)計(jì)的PPMS(the Physical Property Measurement System,PPMS-141)測量，測量溫度范圍為15K-300K。

2 結(jié)果與討論

圖1是(La0.9Gd0.1)4/3Sr5/3Mn2O7樣品的X射線衍射圖。其衍射圖譜由Sr3Ti2O7和ABO3型鈣鈦礦相的衍射峰共同組成(ABO3相的衍射峰用箭頭標(biāo)出)，并且(105)和(110)峰的相對強(qiáng)度發(fā)生了變化，這表明樣品是由Sr3Ti2O7和ABO3結(jié)構(gòu)的相共同組成。由于在雙層鈣鈦礦結(jié)構(gòu)(La0.9Gd0.1)4/3Sr5/3Mn2O7中，離子半徑較小的Gd3+會(huì)優(yōu)先占據(jù)巖鹽層的R位[10,11]，隨著Gd3+的含量的增加，巖鹽層內(nèi)的失配效應(yīng)和應(yīng)力增加，這樣會(huì)導(dǎo)致雙層鈣鈦礦的結(jié)構(gòu)不穩(wěn)定，從而發(fā)生結(jié)構(gòu)相分離生成無限層(ABO3)的鈣鈦礦相。

圖1：室溫下(La0.9Gd0.1)4/3Sr5/3Mn2O7的X射線衍射譜

圖2：0.1T磁場下(La0.9Gd0.1)4/3Sr5/3Mn2O7樣品的磁化強(qiáng)度隨溫度的變化關(guān)系，插圖表示dM/dT與T的關(guān)系

圖3:在溫度范圍內(nèi)，(a)、(b)、(c)和(d)分別為樣品的R-T曲線ln(R/T)—1/T曲線、lnR—1/T曲線和lnR—T-1/4曲線

3 結(jié)論

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