Raman Scattering Study of Ba_2NaNb_<5(1-x)>Ta_<5x>O_<15>

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The concentration dependences of ferroelectricity and ferroelasticity of Ba_2NaNb_<5(1-x)>Ta_<5x>O_<15> were studied by Raman spectroscopy. The A_1(z) mode spectra clearly show the difference between ferro- and paraelectric phases. With the increase of x starting from 0.1, the A_1(z) modes at 278, 640 cm^<-1> and at x=0.1 show softening below x=0.7, and then become higher above x=0.7. It is concluded that the ferroelectric phase becomes a paraelectric one at a concentration between x=0.6 and 0.7. With regard to the ferroelasticity the B_2(y) mode at 32 cm^<-1>, which is coupled to the ferroelasticity, was investigated. When the concentration x increases the mode at 32 cm^<-1> fades and then disappears at a concentration around x=0.9. This strongly suggests that the ferroelastic phase disappears around the concentration of 0.9.
社団法人日本物理学会の論文
1993-04-15