Journal of Electroceramics, 13, 271–275, 2004 C  2004 Kluwer Academic Publishers. Manufactured in The Netherlands. Correlation of Microwave Dielectric Properties and Normal Vibration Modes of Ba(Mg 1/3 Ta 2/3 )O 3 -Series Materials YI-CHUN CHEN, 1,3 HSIU-FUNG CHENG, ∗,1 CHIA-CHI LEE, 1 CHIH-TA CHIA, 1 HSIANG-LIN LIU 1 & I-NAN LIN 2 1 Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan, Republic of China 2 Department of Physics, Tamkang University, Tamsui 251, Taiwan, Republic of China 3 Institute of Physics, Academia Sinica, Taipei 115, Taiwan, Republic of China Submitted March 26, 2003; Revised February 7, 2004; Accepted February 9, 2004 Abstract. Microwave dielectric properties of Ba(Mg 1/3 Ta 2/3 )O 3 -series materials were investigated using Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The normal vibration modes of these spectra were assigned, and the origin of dielectric response of the materials was deduced. Among the prominent normal vibration modes in the FTIR spectra, those which correlated with O-layers and Ba-layers change with Sr-ratio most significantly, whereas in micro-Raman measurements, the A 1g (O) phonon of oxygen-octahedron stretch mode changes with Sr-ratio most profoundly. These results reveal clearly the close relationship between the characteristics of FTIR and Raman spectra of the BMT-series materials and their microwave dielectric properties. Keywords: microwave dielectrics, Raman spectroscopy, FTIR spectroscopy 1. Introduction Complex perovskite compounds with chemical for- mula Ba(B ′ 1/3 B ′′ 2/3 )O 3 , where B ′ = Zn, Mg, Ni or Mn and B ′′ = Nb or Ta, exhibit ultra-low dielectric losses at microwave frequencies [1–3], when the materials possess B ′ -B ′′ 1:2 ordered arrangement with the sym- metry of the structure described by the P ¯ 3m1( D 3 3d ) space group [4]. Since the dielectric properties at mi- crowave frequencies are mainly contributed from the ionic polarization, the study of phonon vibration spec- tra of Ba(B ′ 1/3 B ′′ 2/3 )O 3 has been of particular inter- est [5–12]. Recently, the Raman phonons [13] and the normal mode for resonant peaks in FTIR spectra [14] in Ba(Mg 1/3 Ta 2/3 )O 3 -Ba(Mg 1/3 Nb 2/3 )O 3 , BMT- BMN, materials were unambiguously identified. The change in microwave dielectric properties of the BMT- BMN materials with the composition has been cor- related with the modification on Raman and FTIR spectroscopic characteristics. However, the genuine ∗ To whom all correspondence should be addressed. E-mail: hfcheng@phy03.phy.ntnu.edu.tw mechanism on modifying these spectroscopic behav- iors is still not clear. In this study, we investigated the evolution of the crystal structure of (1 − x )Ba(Mg 1/3 Ta 2/3 )O 3 - x Sr(Mg 1/3 Ta 2/3 )O 3 , (1 − x )BMT-x SMT materials with the composition using Rietvelt method [15], so as to un- derstand the factor which alters the Raman and FTIR spectroscopic characteristics for these materials. By analyzing phonon properties, we attempted to explain the modification on the normal vibration modes for (1 − x )BMT-x SMT due to the change on composition and to correlate the dispersion parameters of the normal modes with their microwave dielectric properties. 2. Experimental Details The (1 − x )BMT-x SMT ceramic samples with x = 0, 1/8, 2/8, 3/8, and 4/8 were prepared by conventional mixed oxide process. These samples were convention- ally sintered at 1600 ◦ C for 3 h. Far-infrared and mid- infrared reflectance spectra, from 20 to 800 cm −1 were taken at room temperature using a Bruker IFS 66v