Chemical Substitution in Ba(RE_1/2Nb_1/2)O₃ (RE = La, Nd, Sm, Gd, Tb, and Y) Microwave Ceramics and Its Influence on the Crystal Structure and Phonon Modes

Abstract

Raman spectroscopy was employed to evaluate the crystal structure and phonon modes of chemically substituted Ba(RE 1/2 Nb 1/2 )O 3 microwave ceramics (RE ) La, Nd, Sm, Gd, Tb, and Y). It was verified that these materials could be divided into tetragonal (ceramics with RE ) Y, Tb, and Gd) and orthorhombic (RE ) Sm, Nd, and La) structures. Lorentzian lines were used to fit the spectra, which presented 9 bands for the first group and 23 bands for the second group of ceramics. The position and width of the phonon modes were determined, and were correlated to the ionic radii and tolerance factors for the different atoms substituted in the B′-site. It is believed that simple rotational distortions of the oxygen octahedra led to the occurrence of structures other than cubic, which is very difficult to detect by X-ray diffraction or even spectroscopic techniques.

Disorder‐induced symmetry lowering in Ba(Y1/2Nb1/2)O3 ceramics probed by Raman spectroscopy

“…It is suggested that the difference in the crystal symmetry is due to a small tilting in the octahedra (anti-phase or in-phase), which is sometimes difficult to determine or quantify by conventional XRD procedures. 2 A previous work in Ba Y 1/2 Nb 1/2 O 3 ceramics, which is a member of the Ba RE 1/2 Nb 1/2 O 3 family, showed that the fully ordered ceramic produced by conventional solidstate route exhibits a tetragonal structure. 2 This conclusive result was possible only through the comparative analysis between XRD and Raman scattering.…”

“…2 A previous work in Ba Y 1/2 Nb 1/2 O 3 ceramics, which is a member of the Ba RE 1/2 Nb 1/2 O 3 family, showed that the fully ordered ceramic produced by conventional solidstate route exhibits a tetragonal structure. 2 This conclusive result was possible only through the comparative analysis between XRD and Raman scattering. Although the structure of fully ordered samples is well established, no information regarding the structure of Ba Y 1/2 Nb 1/2 O 3 ceramics from powders obtained at mild temperatures is available.…”

“…Only very recently conclusive results on this subject were achieved by using X-ray diffraction (XRD) as well as Raman and Fourier-transform infrared spectroscopies. 2 In this respect, the polar optical phonons determine the highfrequency dielectric response, which in turn depends on the sample structure (intrinsic contributions) together with extrinsic contributions coming from space charges, domain walls and imperfections linked to the sample morphology. 2 -5 Thus, these ceramic materials are very sensitive to the processing conditions (powder synthesis and sintering), which affect directly the three key properties for applications as dielectric resonators: permittivity, temperature coefficient of the resonant frequency, and dielectric loss.…”

Spin-phonon coupling in Gd(Co1/2Mn1/2)O3 perovskite

“…The conclusive explanation of this particular difference remains unraveled and calls for further investigations to the entire family, including ordered (conventionally typed RE2CoMnO6) and disordered (conventionally typed RE(Co1/2Mn1/2O3) compounds.. In this Letter, we have investigated the spin-phonon 4 coupling in the Gd(Co1/2Mn1/2)O3 (GCMO) perovskite using temperature-dependent Raman spectroscopy, which has been an important tool to investigate order, magnetic transitions, and spin-phonon coupling in perovskites [12,15,[18][19][20][21][22].Polycrystalline samples of GCMO were synthesized by polymeric precursor method [23] using cobalt acetate tetrahydrate (C4H6CoO4•4H2O, Sigma Aldrich), manganese nitrate hydrate (MnN2O6•xH2O, Sigma Aldrich) and gadolinium oxide (Gd2O3, Sigma, Aldrich) as high purity metals sources. The resin and puff (powder obtained by the resin precalcination) were obtained following the steps described elsewhere [21].…”

Relaxations in Ba2BiSbO6 double complex perovskite ceramics

“…[8][9][10][11][12][13][14] For the 1:1 ratio case, one common application is as microwave dielectrics. [15][16][17][18][19] For this ratio the structure normally shows ordering in the BЈ and BЉ ion distributions that occur in an alternate form along with the three crystalline axes. This ordering is commonly called NaCl ordered and the aristotype structure is cubic with Fm3m symmetry.…”