内化学压力对传输性质的影响及传感器应用中的TCR
Effect of internal chemical pressure on transport properties and TCR for sensors applications
摘要：
本文研究了固相反应法制备的（Nd_（0.7-x）Lax）Sr_（0.3）MnO_3（x = 0，0.1和0.2）锰氧化物的结构和输运性质。发现这些化合物以斜方晶结构形式结晶。在A位取代Nd的La的影响使金属到半导体/绝缘体转变温度（TMI）峰向室温移动，其中x = 0、0.1和0.2。在（Nd 0.7-xLax）0.7Sr 0.3MnO3锰氧化物（即（Nd 0.5La 0.2）0.7Sr 0.3MnO3）中以x = 0.2制备的组合物在接近室温的289 K下观察到TMI。与母体化合物相比，化合物的TCR值的最大百分比随着平均半径而增加<r_A>，但%TCR在x = 0.1和0.2时略微相等。在x = 0.1和0.2时，最大%TCR值几乎与A位平均半径无关<r_A>。用不同的理论模型对电阻率数据进行了探讨，得出了在低温下，（铁磁金属区）导电机制可能是由于电子-电子、电子-声子和电子-磁振子散射的综合作用，而在顺磁半导体区，电阻率随温度的变化由（1）Mott变程跳跃机制解释，（2）绝热小极化子跃迁;（3）热激活跃迁。极化子跳跃和热激活能随A位离子平均半径的增大而减小<rA>。一个适当的启示所观察到的行为进行了详细讨论。
英文摘要：
In this work, the structural and transport properties of (Nd0.7-xLax)Sr0.3MnO3 manganites with x = 0, 0.1 and 0.2 prepared by solid state reaction route are studied. These compounds are found to be crystallized in orthorhombic structural form. The influence of La substitution in place of Nd at A-site shifts the metal to semiconductor/insulator transition temperature (TMI) peak towards room temperature with x = 0, 0.1 and 0.2. A composition prepared with the value of x = 0.2 in (Nd0.7-xLax)0.7Sr0.3MnO3 manganites (i.e. (Nd0.5La0.2)0.7Sr0.3MnO3), TMI was observed at 289 K which is close to room temperature. The maximum percentage of TCR values of compounds are increasing with average radius <r_A> but %TCR are slightly equal in x = 0.1 and 0.2 as compared to the parent compound. The maximum %TCR value is almost independent with A-site average radius <r_A> in x = 0.1 and 0.2. The electrical resistivity data are explored by different theoretical models and it has been concluded that at low temperature (ferromagnetic metallic region) conduction mechanism presumably due to the combined effect of electron-electron, electron-phonon and electron-magnon scattering, while in paramagnetic semiconducting regime, the variation of resistivity with temperature are explained by (1) Mott variable range hopping mechanism, (2) Adiabatic small polaron hopping and (3) Thermally activated hopping. The polaron hopping and thermal activation energies are decreasing with increase of an average A-site ionic radius (<rA>). An appropriate enlightenment for the observed behavior is discussed in detail.
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