钛酸锶钡拉曼光谱的理论计算与实验研究

钛酸钡是一种重要的铁电体，在居里温度130 ℃附近介电常数最大，为了降低钛酸钡的居里温度，通常在钛酸钡中掺杂锶.采用水热合成法制备了钛酸锶钡粉末，并且建立2×2×1的超晶胞进行第一性原理计算.随着锶掺杂量的增加，其XRD衍射峰向右偏移，说明钛酸锶钡的晶胞结构逐渐从四方相转变到立方相.计算结果表明:随着锶掺杂量增加，钛酸锶钡的晶胞参数逐渐减小；晶胞参数c与a的比值逐渐减小，与实验相符；Raman光谱特征峰的强度逐渐减弱，说明掺杂后钛酸锶钡的自发极化程度逐渐减弱，Ti和O分别偏离晶胞体心和面心的位移逐渐减小.由于掺杂后钡原子被比其原子半径小的锶原子取代，使得晶胞参数变小，阻碍了Ti的自发偏移，Ti只需要较低的热振动能即可克服与O的库仑作用，稳定位于晶胞体心，居里温度(居里点)随之下降.

Theoretical and Experimental Studies of Raman Spectroscopy of Barium Strontium Titanate

Barium titanate is an important ferroelectric and its dielectric constant is the highest near the Curie point of 130 ℃. In order to reduce the Curie point of barium titanate, strontium is usually doped in barium titanate. Barium titanate powder was prepared with hydrothermal synthesis, and a 2×2×1 supercell was established for first-principles calculations. The rightward shift of the XRD diffraction peak with the increase of doped strontium indicates that the unit cell structure of barium strontium titanate gradually changes from tetragonal phase to cubic phase. The calculated results show that the unit cell parameters of barium titanate are gradually reduced. The ratio of the unit cell parameters c to a gradually decreases, which is consistent with the experiment; the gradual weakening of the Raman spectral peak indicates that the degree of spontaneous polarization of barium titanate is gradually weakened. It is found that the displacements of Ti and O from the body-center and face-center respectively are gradually reduced. Because the atomic radius of strontium is smaller than that of barium, after the barium is replaced by strontium in the unit cell, the unit cell parameters will become smaller, which hinders the spontaneous displacement of Ti. Ti only needs lower thermal vibration energy to overcome the Coulombic interaction with O and located in the center of the unit cell steadily. So the Curie temperature(Curie points) of barium strontium titanate will fall with the increase of doped strontium.