| In recent years, ABO3oxides with perovskite structure (A is the cation with larger radius like Na+, K+, Ca2+, Sr2+, Ba2+and rare-earth cations, B is the cation with smaller radius like Ti4+, Nb3+, Mn4+, Fe3+, Tb4+and Zr4+) are used in many fields due to their distinctive electronic structure and chemical durability. People pay much attention on their magnetism, gas-sensing properties and multiferroic.Multiferroics are compounds in which the ferroelectric (anti-ferroelectric) order and ferromagnetic (anti-ferromagnetic) order coexist simultaneously in a certain temperature range. The coupling effects between these two order structures are focus of study. However, in oxides with perovskite structure, the conventional mechanism for cation off-centering in ferroelectrics requires formally empty d orbitals, and the formation of magnetic moments usually results from partially filled d orbitals. Recently, d0room temperature in undoped nanocrystalline oxides has been found which may stems from vacancies. In present work, we study the room temperature magnetic and multiferroic properties of the ferroelectric material PZT.In perovskite NdFeO3, the ordering of Fe3+magnetic moments is antiferromagnetic with the Neel temperature TN=760K, which has been shown in the neutron diffraction studies. There are two different types of magnetic ions:Fe3+, Nd3+and three super-exchange interactions:Fe-Fe, Nd-Fe, and Nd-Nd. It is the competition of these interactions that leads to a few interesting phenomena in NdFeO3. In the present paper, we study the magnetic property of NdFeO3in order to get clear understanding. At the same time, we discuss the dielectric property of NdFeO3.Compared to the single metal oxides, the properties of ABO3oxides with perovskite structure, such as sensitivity, selectivity and the optimal temperature, can be changed by choosing different elements at A or/and B sites or using other elements to substitute A or/and B, which is very flexible. The oxides which have been studied most are LnFeO3(Ln represents rare-earth elements). It is always to partially substitute Ln by some lower valence elements like Ca, Sr, Ba, and Pb. In present work, we study the gas-sensing properties of Nd1-xCaxFe03system.The abstract of our results as follows:1. Structure:We prepared PbZr0.1Tio903, PbZr0.2Ti0.8O3, Nd1-xCaxFe03(x=0,0.1,0.2,0.3,0.4) nano-materials by sol-gel method. In order to compensate the lead loss during sintering process, excess Pb(CH3COO)2·3H2O (3%) was added. X-ray diffraction analysis indicated that all the samples are of single phase with perovskite structure.2. The weak ferromagnetism is detected in PbZr0.1Ti0.9O3and PbZr0.2Ti0.8O3nanocrystalline materials at room temperature. It may stems from oxygen vacancies in samples. Both ferroelectric and ferromagnetic properties are detected in PbZr0.1Ti0.9O3pellet (1150℃,2h) and PbZr0.2Ti0.8O3pellet (1000℃,1h), respectively.△ε/εr(0) is18.3%in PbZr0.1Ti0.9O3pellet and25.3%in PbZr0.2Ti0.8O3pellet.3. The100Oe ZFC and FC magnetizations as functions of temperature for the NdFeO3pellet calcined at1000℃are detected. The intrinsic antiferromagnetic and concomitantly ferromagnetic of the pellet are shown in magnetic hysteresis loop at50K. The pellet is intrinsic antiferromagnetic at4K and300K. There is a peak of the dielectric constant in εr-T curve between50-125K.4. The resistance of Nd1-xCaxFe03-based sensor reduces and the gas-sensing properties are improved with Ca dopants. The responses of the Ndo.9Ca0.1Fe03-based sensor to600ppm ethanol and acetone were about158.4at220℃and61.7at240℃, respectively. The Nd0.9Ca0.1FeO3-based sensor showed good sensitivities and selectivity to ethanol and acetone. |
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