【摘要】：具有Cr~(4+)離子以及CrO6八面體配位的氧化物由于處于絕緣體和金屬的臨界狀態(tài),表現(xiàn)出奇異的電子態(tài)和物性。本文在高溫高壓條件下合成了幾類A-Cr-O(A為堿土元素)體系相關(guān)的化合物,并表征了其結(jié)構(gòu)和物性。具體包括以下幾方面：(1)制備了Sr_xCa_(1-x)CrO_3(0≤x≤1)系列單晶樣品。用單晶衍射儀測(cè)試了樣品結(jié)構(gòu),隨著x增加,系列樣品經(jīng)歷了由正交到四方最后到立方的結(jié)構(gòu)轉(zhuǎn)變。除了SrCrO_3,系列樣品均出現(xiàn)反鐵磁轉(zhuǎn)變,奈爾溫度隨x增加而減小,在x=0、1/6和1/3的單晶中測(cè)試出明顯的磁各向異性。單晶電輸運(yùn)測(cè)試顯示系列樣品均表現(xiàn)為半導(dǎo)體行為。通過制備和表征一系列的單晶樣品,準(zhǔn)確得出奈爾溫度與樣品組分相圖,從電輸運(yùn)角度佐證了樣品的局域電子態(tài),并為后續(xù)的深入研究打下了基礎(chǔ)。(2)制備了La_xCa_(1-x)CrO_3(0≤x≤1)系列多晶樣品。GSAS精修了結(jié)構(gòu),均為正交相,空間群Pbnm,隨著x增加,晶格常數(shù)變大。隨著x增加,系列樣品經(jīng)歷了由C型反鐵磁到G型反鐵磁的轉(zhuǎn)變,奈爾溫度隨La含量的變化率dTN/dx～210K/x。電阻率隨x增加而變大,逐漸由半導(dǎo)體轉(zhuǎn)變?yōu)榻^緣體。該體系顯示出Cr離子由Cr~(4+)向Cr~(3+)的轉(zhuǎn)變對(duì)樣品磁電性質(zhì)的調(diào)控作用。(3)制備了單層鈣鈦礦結(jié)構(gòu)的Ca_2CrO_4和Sr_2CrO_4,其中Sr_2CrO_4合成了單晶樣品。Ca_2CrO_4為四方結(jié)構(gòu),空間群I41/acd；直流和交流磁化率測(cè)試顯示Ca_2CrO_4為自旋玻璃磁性；常壓和高壓下均表現(xiàn)出絕緣體行為。Ca_2CrO_4的合成進(jìn)一步豐富了A-Cr-O體系,并顯示出結(jié)構(gòu)畸變對(duì)長程磁有序的抑制。Sr_2CrO_4為K_2NiF_4結(jié)構(gòu),空間群I4/mmm;在95K出現(xiàn)一個(gè)自旋軸沿c方向的弱反鐵磁轉(zhuǎn)變,單晶樣品觀察到了明顯的磁各向異性；電阻測(cè)試結(jié)果同樣在常壓和高壓下都顯示為絕緣體。
[Abstract]:The oxides with Cr~ (4) ion and CrO6 octahedral coordination show strange electronic states and physical properties due to their critical state of insulators and metals. In this paper, several kinds of compounds related to A-Cr-O (A as alkali soil element) system were synthesized under high temperature and high pressure, and their structures and physical properties were characterized. The main contents are as follows: (1) Sr_xCa_ _ (1-x) CrO_3 (0 鈮，

本文編號(hào)：2216907