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首页> 外文期刊>Physical review >Ferroelectric phase transition in barium titanate nanoparticles
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Ferroelectric phase transition in barium titanate nanoparticles

机译：钛酸钡纳米粒子中的铁电相变

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Size-dependent changes were found in the ~(137)Ba NMR spectra of ensembles of very small BaTiO_3 particles. The NMR line shapes were studied at different Larmor frequencies over a broad temperature range. In (he tetragonal phase, the NMR lines may be decomposed into a contribution typical for the line shape of bulk samples ("ordered" part) and a part in which the tetragonal symmetry is no longer visible ("disordered" part). Both contributions reveal typical changes when the temperature is varied in the range of the tetragonal phase, i.e., between approximately 400 and 300 K. The "ordered" part reveals a first-order phase transition at temperature T_f which decreases when the particle size becomes smaller. As is known, in the case of bulk material the quadrupole coupling constant C_Q may be related to the order parameter (spontaneous polarization P_S). Therefore, for all samples the temperature dependence of the C_Q in the "ordered" part was studied in the whole tetragonal phase. Its temperature dependence below T_f, with a jump at the first-order phase transition, can be described by an exponential law C_Qα(T_f-T)β+const for T
机译：在非常小的BaTiO_3粒子的集合的〜（137）Ba NMR光谱中发现了尺寸相关的变化。在较宽的温度范围内，在不同的拉莫尔频率下研究了NMR线形。在（四方相中），NMR线可分解为大块样品的线形的典型贡献（“有序”部分）和不再可见四方对称的部分（“无序”部分）。 “有序的”部分揭示了温度在T_f处的一阶相变，当颗粒尺寸变小时，该相变会减小，当温度在四方相的范围内变化时，即在大约400至300 K之间变化时，典型的变化。众所周知，在散装材料的情况下，四极耦合常数C_Q可能与阶跃参数（自发极化P_S）有关，因此，对于所有样品，“有序”部分中C_Q的温度依赖性都在整个四边形中进行了研究。它的温度依赖性低于T_f，并在一阶相变时跃迁，可以用指数定律C_Qα（T_f-T）β+ const来描述T

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