Microstructures in Pb(In 1/2 Nb 1/2 )O 3 with the Perovskite B-site Randomness
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Microstructures in Pb(In1/2Nb1/2)O3 with the Perovskite B-site Randomness S. Mori1,*, K. Kurushima2, K. Kobayashi1, H. Ohwa3, N. Yasuda3 and K. Ohwada4 1
Osaka Prefecture University, Sakai, Osaka 599-8531, Japan Toray Research Center, Ohtsu, Shiga 520-8567, Japan. 3 Gifu University, Gifu 501-1193, Japan. 4 Spring 8, Japan Atomic Energy Agency, Sayo-cho, Hyogo 679-5148, Japan *[email protected] 2
ABSTRACT We have investigated microstructures in both the antiferroelectric (AFE) and relaxor states of Pb(In1/2Nb1/2)O3 (PIN) with the perovskite structure by a transmission electron microscopy (TEM). Electron diffraction (ED) experiments revealed that the AFE state is characterized as the modulated structure with the modulation vector of q=1/4 1/4 0. High-resolution TEM images clearly show the coexistence of two types of domains consisting of the modulated and the nonmodulated structures with the 100 ~ 200 nm size. On the other hand, in the relaxor state there appear two types of diffuse scatterings in the ED patterns. One is diffuse spots at the 1/2 1/2 0type reciprocal positions and the other is diffuse streaks elongating along the direction around the fundamental spots. The real-space TEM images clearly demonstrate the presence of nanodomains with the average size of ~ 5 nm. These nanodomains in the relaxor state should be responsible for the characteristic dielectric properties. INTRODUCTION Relaxor ferroelectrics are characterized by having highly frequency dependent dielectric response (ε) with a broad maximum in temperature. Complex lead-based perovskitetype ferroelectric materials Pb(B,B’)O3 with the perovskite structure have been of fundamental and practical interest because of their unusual dielectric and piezoelectric response and great potential for industrial applications [1,2,3,4]. The chemical disorder on the B-site in the perovskite structure should have crucial influence on the relaxor behaviors. In relaxor ferroelectrics such as Pb(Zn1/3Nb2/3)O3 (PZN) and Pb(Mg1/3Nb2/3)O3 (PMN), Zn2+/Mg2+ and Nb5+ take a 1 : 2 ratio on the B-site to keep an average valence of 4+ for charge conservation. Charge neutrality would lead to chemical order on the B-site. Practically, chemical ordered regions (COR’s) with Mg:Nb=1:1 gives rise to effective strain field, which have some influence on the formation of polar nano regions (PNR’s) in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3. To understand characteristic features of relaxor ferroelectrics, it is crucial to clarify roles of the COR and PNR on the relaxor behaviors. In Pb(In1/2Nb1/2)O3 (PIN), the temperature dependence of dielectric constant strongly depends on the chemical order parameter S2, which is defined as S2=(I1/2, 1/2, 1/2/I111)obs/(I1/2, 1/2, 1/2/I111)cal. Note that I1/2, 1/2, 1/2 and I111 denote the intensities of 1/2, 1/2, 1/2 and 1 1 1 reflections. The states of PIN can be classified as the antiferroelectric (AFE) state with S2>0.7, the ferroelectric state with 0.4
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