Trepakov V A, Potůček Z, Makarova M V, Dejneka A, Sazama P, Jastrabik L, Bryknar Z
Institute of Physics ASCR, v. v. i., Na Slovance 2, CZ-182 21 Praha 8, Czech Republic. A F Ioffe Physico-Technical Institute RAS, 194 021, Saint Petersburg, Russia.
J Phys Condens Matter. 2009 Sep 16;21(37):375303. doi: 10.1088/0953-8984/21/37/375303. Epub 2009 Aug 19.
The crystal structure, optical absorption, and photoluminescence of chromium impurity centers were studied in nanocrystalline SrTiO(3):Cr (0.1 mol%) powders with average particle size within the range 13-100 nm prepared by the Pechini-type polymeric sol-gel method. Only the presence of a cubic perovskite phase of O(h)(1) symmetry was proved for the powders at room temperature, by means of x-ray diffraction. The lattice constant a = 3.910 Å, larger than that of bulk SrTiO(3) crystals (a = 3.905 Å), was found for nanoparticles with the size about 20 nm. The optical absorption edge and the zero-phonon R-line ([Formula: see text]) of luminescence of the octahedral Cr(3+) centers shifted to higher energies with decreasing nanoparticle size. These size effects were regarded as intrinsic to SrTiO(3). An unusual and large temperature shift of the R-line position very similar to the 'dielectric related' one of the bulk crystals was observed for all powders, evidencing their quantum paraelectric behavior. However, the powders with the average particle size about 13 and 20 nm did not reveal completely reproducible behavior of the R-line position at low temperatures. This instability was considered a possible manifestation of a low-temperature phase transition in small enough SrTiO(3) nanoparticles.
采用佩琴尼型聚合物溶胶 - 凝胶法制备了平均粒径在13 - 100 nm范围内的纳米晶SrTiO₃:Cr（0.1 mol%）粉末，研究了其中铬杂质中心的晶体结构、光吸收和光致发光特性。通过X射线衍射证明，室温下这些粉末仅存在具有O(h)₁对称性的立方钙钛矿相。对于尺寸约为20 nm的纳米颗粒，发现其晶格常数a = 3.910 Å，大于块状SrTiO₃晶体的晶格常数（a = 3.905 Å）。随着纳米颗粒尺寸减小，八面体Cr³⁺中心发光的光吸收边和零声子R线（[公式：见原文]）向更高能量移动。这些尺寸效应被认为是SrTiO₃所固有的。对于所有粉末，均观察到R线位置出现了与块状晶体中“与介电相关”的异常且较大的温度偏移，这证明了它们的量子顺电行为。然而，平均粒径约为13和20 nm的粉末在低温下并未显示出R线位置完全可重复的行为。这种不稳定性被认为可能是足够小的SrTiO₃纳米颗粒中低温相变的一种表现。
