Pan Zhao, Chen Jun, Jiang Xingxing, Lin Zheshuai, Zhang Linxing, Fan Longlong, Rong Yangchun, Hu Lei, Liu Hui, Ren Yang, Kuang Xiaojun, Xing Xianran
Department of Physical Chemistry, University of Science and Technology Beijing , Beijing 100083, China.
BCCRD, Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
Inorg Chem. 2017 Mar 6;56(5):2589-2595. doi: 10.1021/acs.inorgchem.6b02761. Epub 2017 Feb 16.
Zero thermal expansion (ZTE) behavior is rare but important for both fundamental studies and practical applications of functional materials. Until now, most available ZTE materials are either electrical insulating oxides or conductive metallic compounds. Very few ZTE materials exhibit the semiconductor feature. Here we report a ZTE in a semiconducting ferroelectric of 0.6PbTiO-0.4Bi(CoTi)O. Its unit cell volume exhibits a negligible change over a broad temperature range from room temperature to 500 °C. The ZTE is supposed to be correlated with the spontaneous volume ferroelectronstriction. Intriguingly, the present ZTE material also exhibits the semiconducting characteristic accompanied by negative temperature coefficient of resistance. The mechanism of electric conduction is attributed to the electronic hopping from one ion (Ti) to another (Ti). The semiconductor nature has also been confirmed by the noticeable visible-light absorption with the relatively lower band gap (E) value of 1.5 eV, while the ferroelectric property can be well-maintained with large polarization. The first-principles calculations reveal that the drastically narrowed E is related to the Co-Ti substitution. The present multifunctional material containing ZTE, semiconducting, and ferroelectric properties is suggested to enable new applications such as the substrate for solar conversion devices.
零热膨胀（ZTE）行为虽然罕见，但对于功能材料的基础研究和实际应用都很重要。到目前为止，大多数现有的ZTE材料要么是电绝缘氧化物，要么是导电金属化合物。很少有ZTE材料具有半导体特性。在此，我们报道了一种0.6PbTiO-0.4Bi(CoTi)O半导体铁电体中的ZTE。其晶胞体积在从室温到500°C的宽温度范围内变化可忽略不计。这种ZTE被认为与自发体积铁电致伸缩有关。有趣的是，目前的ZTE材料还表现出半导体特性，并伴有负电阻温度系数。导电机制归因于电子从一个离子（Ti）跳跃到另一个离子（Ti）。半导体性质也通过具有1.5 eV相对较低带隙（E）值的明显可见光吸收得到证实，而铁电性能可以通过大极化得到很好的保持。第一性原理计算表明，急剧变窄的E与Co-Ti取代有关。这种包含ZTE、半导体和铁电性能的多功能材料有望实现新的应用，如太阳能转换器件的衬底。
