钙掺杂对铬酸镧热膨胀系数的影响

Effect of Ca-Doping on Coefficient of Thermal Expansion of Lanthanum Chromites

利用固相法合成的铬酸镧粉制备铬酸镧样品。研究了钙掺杂量对铬酸镧样品热膨胀系数的影响。结果表明:当钙掺杂铬酸镧时,Ca2+于A位取代La3+,引起A位离子半径减小,晶胞参数发生变化,同时Cr3+变价形成Cr4+,引起了O2–—O2–和Cr3+—O2–键长、键角和键能相应改变,从而对铬酸镧样品的热膨胀系数和相变温度造成影响;从室温到1000℃,铬酸镧的热膨胀系数随钙掺杂量增加而增大,由正交结构向菱形结构转变的相变温度随钙掺杂量增加呈线性提高。

The lanthanum chromites samples were prepared by the powders synthesized by a solid-state reaction. The effect of Ca-doping on coefficient of thermal expansion（CTE） of lanthanum chromites was studied. The results showed that with the Ca-doping, A site atom La^3＋ in the LaCrO3 would be replaced by the Ca^2＋, the radius of A site was reduced and crystal parameter was changed. At the same time, the bond length, bond angel and bond energy of O^2--O^2-, Cr^3--O^2- were changed due to the changing of Cr^3＋ to Cr^4＋. Between room temperature to 1 000 ℃, the CTE of lanthanum chromites increased with the increase of Ca-doping content, also the phase transformation temperature of lanthanum chromites from the orthogonal structure to rhombic structure linearly increased with Ca-doping content.