Structural ordering and dielectric properties of Ba3CaNb2O9-based microwave ceramics

2020

J Raman Spectroscopy

Ba3MgNb2O9 is a double perovskite niobate with a trigonal structure with space group D3d3. Such a niobium‐based compound has a great potential for applications as microwave dielectrics in the telecommunication industry. In this work, we report the lattice dynamics calculation results using a Short‐Range Force Field Model and Density Functional Theory to represent the optical phonon modes at Γ‐point of the Brillouin zone. The classical method uses the nearest neighbor interactions through the interatomic force constants to describe the local order for Raman and infrared spectra. At the same time, density functional theory methods took into account two functionals (PBE and B3LYP) in order to provide the optical modes through second derivatives of the total energy. In both methods, theoretical optical modes are in good agreement with reported experimental data. The combination of both classical and quantum theoretical methods provided basis for a systematic discussion on the origin of the optical modes including the prediction of the dielectric tensor. We believe that this work presents useful information about the structural and vibrational characterization of Ba3MgNb2O9 perovskite and possible targeting for its application as microwave dielectrics for the communication technology.

Section: Resultssupporting

confidence: 81%

Section: Resultsmentioning

confidence: 94%

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Optical phonon modes in 1:2 ordered trigonal Ba₃MgNb₂O₉ perovskite: Synergy of both classical and quantum methods

Ferrer

2020

J Raman Spectroscopy

“…The signature of this phenomenon can be detected in Fig. 1 [24,38]. The detection of those superlattice reflections is an evidence for the long range 1:1 and 1:2 orderings in the BCNO ceramics [39].…”

Section: Cation Ordering At B-sitementioning

confidence: 99%

Ordering effect on the electrical properties of stoichiometric Ba3CaNb2O9-based perovskite ceramics

Bezerra

2017

Ceramics International

Self Cite

Cation ordering is most common process detected in A 3 B'B'' 2 O 9 -based complex perovskites. Some important physical features of this system are due to the B-site ordering at long and short range. For microwave applications as filters and resonators, the 1:2 order is more appropriate. Otherwise, the oxygen vacancies and 1:1 order are considered the main factors behind the good performance of nonstoichiometric A 3 B' 1+x B'' 2-x O 9-δ -based ceramics as proton conductors. Until now, however, there are no available reports regarding the isolated effects of B-site order at long range on the electrical properties of stoichiometric systems. This work reports the preparation of 1:1 and 1:2 fully-ordered Ba 3 CaNb 2 O 9 ceramics. Here, we combine the Raman scattering and group-theory calculations to distinguish the fingerprints of the 1:1 and 1:2 orders. The electric properties of the ordered Ba 3 CaNb 2 O 9 are analyzed in terms of a phenomenological model based on a parallel combination of a resistor, constant phase element, and capacitor. In particular, the conductivity relaxation ascribed to the grain is due to the oxygen vacancies. Besides, we found that the 1:1 order increases the dc conductivity, but not enough to account the good performance reported for the non-stoichiometric Ba 3 Ca 1+x Nb 2-x O 9-δ -based proton conductors.

“…In the 1:1 ordered cubic perovskites, the structural disorder usually appears as antisite defects in which 4 a and 4 b positions are partially filled by B′ and B″ cations. Unlike the case of the 1:2 ordered perovskites presenting the two‐phonon behavior for the A 1g breathing mode, antisite process only induces a one‐phonon behavior in 1:1 ordered systems. It means that the effect of disorder can be seen by following the peak parameters such as intensity I 0 , position ν and width Γ .…”

Section: Resultsmentioning

confidence: 86%

Calculation of the optical phonons in ordered Ba₂MgWO₆ perovskite using short‐range force field model

Bezerra

2018

J Raman Spectroscopy

Self Cite

Ba2MgWO6 is a double perovskite tungstate presenting a cubic structure with cubic space group Oh5. This B‐site ordered system has potential applications as microwave ceramics in communication systems. Here, we present our results on the lattice dynamics calculations using short‐range force field model to describe both Raman (A1g ⊕ Eg ⊕ 2F2g) and infrared (4F1u) optical phonons at Γ‐point of the Brillouin zone in Ba2MgWO6 perovskite. Short‐range interactions were parameterized through four stretching and three bending force constants in light of the Wilson's GF‐matrix method. Satisfactory agreement between experimental and calculated vibrational data was found. We have used the potential energy distribution (PED) coefficients to determine the contribution of each force constant to the optical modes. The PED analysis elucidates that the W atom has a nonnegligible contribution in describing both A1g breathing and Last‐type (F1u) modes. Such a modeling provided insights into vibrational modes, enabling correlation between optical phonons, disorder effects, and physical properties for applications.