scholarly journals Dielectric Characterization at High Temperature of Iron Doped Potassium Strontium Niobate Ceramic by Impedance Spectroscopy

2015 ◽  
Vol 820 ◽  
pp. 187-192
Author(s):  
Caio Vinicius de Lima ◽  
Marcos Augusto Lima Nobre ◽  
Silvania Lanfredi
Keyword(s):  
Impedance Spectroscopy ◽  
Room Temperature ◽  
Tungsten Bronze ◽  
Type Structure ◽  
Iron Cation ◽  
Tetragonal Tungsten Bronze ◽  
Dielectric Characterization ◽  
Iron Doped ◽  
Host Structure ◽  
Modified Polyol Method

Tetragonal Tungsten Bronze structure TTB-type structure has attracted interest by the high anisotropy of the crystal structure. The dielectric characterization of iron-doped niobate of TTB-type structure, with stoichiometry KSr2(Fe0.25Nb4.75)O15-δ, prepared by Modified Polyol Method was investigated. Nanocrystalline single phase powders were obtained after calcination of the precursor powder at 1150 °C for 10 hours in an oxygen atmosphere. The dielectric characterization was performed by impedance spectroscopy, from room temperature to 600 °C, in the frequency range of 5 Hz to 13 MHz. The permittivity values obtained for KSr2(Fe0.25Nb4.75)O15-δshowed superior to the permittivity values of the KSr2Nb5O15host structure in all temperature range investigated. At room temperature, the permittivity values (2100) of KSr2(Fe0.25Nb4.75)O15-δis two times the permittivity values of KSr2Nb5O15. The substitution of niobium cation by iron cation in the KSr2Nb5O15host structure showed a suppression of the ferroelectric (P4bm)→paraelectric (P4/mbm) phase transition.

scholarly journals Selective Occupancy of Sites by Rare Earths in K2Nd(1-X)EuxNb5O15 Nanopowders, where X = 0, 0.0025, 0.025, 0.05 and 0.1, Prepared by Modified Polyol Method

2015 ◽  
Vol 820 ◽  
pp. 361-366
Author(s):  
Eliane Ayumi Namikuchi ◽  
Marcos Augusto Lima Nobre ◽  
Silvania Lanfredi
Keyword(s):  
Rietveld Method ◽  
Structural Parameters ◽  
Tungsten Bronze ◽  
Average Crystallite Size ◽  
Polyol Method ◽  
Type Structure ◽  
Tetragonal Symmetry ◽  
Tetragonal Tungsten Bronze ◽  
Host Structure ◽  
Modified Polyol Method

Niobates with tetragonal tungsten bronze TTB-type structure have presented great technological potential due to their dielectric, ferroelectric, pyroelectric properties. The preparation by the modified polyol method and structural characterization of K2Nd(1-x)EuxNb5O15 nanopowders, where x = 0; 0.0025; 0.025; 0.05 e 0.1, were investigated. The structural parameters were analyzed as a function of concentration of europium ions in the K2NdNb5O15 host structure using the Rietveld method. From structural parameters was determined the TTB-type structure with tetragonal symmetry, where the pentagonal sites is occupied by K+ and Eu3+ ions and tetragonal sites is occupied only by Nd3+ ions. The addition of europium in the host structure led to a decrease in the lattice parameters, compatible with the increasing degree of distortion of NbO6 polyhedra. The average crystallite size showed values between 18.25 and 26nm.

Incommensurate modulation of calcium barium niobate (CBN28 and Ce:CBN28)

2012 ◽  
Vol 68 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Heribert A. Graetsch ◽  
Chandra Shekhar Pandey ◽  
Jürgen Schreuer ◽  
Manfred Burianek ◽  
Manfred Mühlberg
Keyword(s):  
Crystal Structures ◽  
Tungsten Bronze ◽  
Atomic Displacement ◽  
Type Structure ◽  
Formula Unit ◽  
Tetragonal Tungsten Bronze ◽  
First Order ◽  
Oxygen Coordination ◽  
Incommensurate Modulation ◽  
Atomic Displacement Parameters

The incommensurately modulated crystal structures of Ca0.28Ba0.72Nb2O6 (CBN28) and Ce0.02Ca0.25Ba0.72Nb2O6 (Ce:CBN28) were refined in the supercentred setting X4bm(AA0,−AA0) of the 3 + 2-dimensional superspace group P4bm(aa½,−aa½). Both compounds are isostructural with a tetragonal tungsten bronze-type structure. The modulation of CBN28 consists of a wavy distribution of Ba and Ca atoms as well as vacancies on the incompletely occupied Me2 site with 15-fold oxygen coordination. The occupational modulation is coupled with a modulation of the atomic displacement parameters and a very weak modulation of the positional parameters of Me2. The surrounding O atoms show strong displacive modulations with amplitudes up to ca 0.2 Å owing to the cooperative tilting of the rigid NbO6 octahedra. The Me1 site with 12-fold coordination and Nb atoms are hardly affected by the modulations. Only first-order satellites were observed and the modulations are described by first-order harmonics. In Ce:CBN28 cerium appears to be located on both the Me2 and Me1 sites. Wavevectors and structural modulations are only weakly modified upon substitutional incorporation of 0.02 cerium per formula unit of calcium.

Structures and phase transitions in barium sodium niobate tungsten bronze (BNN)

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Thomas A. Whittle ◽  
Christopher J. Howard ◽  
Siegbert Schmid
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Tungsten Bronze ◽  
Standard Setting ◽  
Experimental Results ◽  
Temperature Structure ◽  
Sodium Niobate ◽  
Tetragonal Tungsten Bronze ◽  
Space Group ◽  
The Subject

The room-temperature structure of the filled tetragonal tungsten bronze, Ba2NaNb5O15 (BNN), has been the subject of a number of studies, and these studies have given an almost corresponding number of different results. From a group theoretical examination of the different possibilities and a review of the published experimental results we conclude that the room-temperature structure is that proposed by Labbé et al. [J. Phys. Condens. Matter (1989), 2, 25–43] in the space group Bbm2 (Ama2 in standard setting) on a 2\sqrt{2}a × \sqrt{2}a × 2c cell. Upon heating, the structure remains ferroelectric but becomes tetragonal (space group P4bm) at 550 K, then paraelectric (space group P4/mbm) at and above 860 K.

Study of the Influence of Eu3+ Ions in the Bandgap of K2NdNb5O15 Nanopowders

2015 ◽  
Vol 820 ◽  
pp. 378-383
Author(s):  
Eliane Ayumi Namikuchi ◽  
Ana Maria Pires ◽  
Marcos Augusto Lima Nobre ◽  
Silvania Lanfredi
Keyword(s):  
Diffuse Reflectance ◽  
Diffuse Reflectance Spectroscopy ◽  
Tungsten Bronze ◽  
Small Variation ◽  
Rare Earth Ions ◽  
Tetragonal Symmetry ◽  
Bandgap Energy ◽  
X Ray Diffraction ◽  
Tetragonal Tungsten Bronze ◽  
Modified Polyol Method

Ferroelectric semiconductors oxides with tetragonal tungsten bronze TTB-type structure doped with rare earth ions have been investigated in recent years due their promising optical properties. K2Nd(1-x)EuxNb5O15 nanopowders, where x = 0, 0.0025, 0.025, 0.05 and 0.1 were synthesized by the modified polyol method and characterized by X-ray diffraction and diffuse reflectance spectroscopy UV-Vis. Single phase and crystalline powders of tetragonal symmetry with non-centrosymmetric space group P4bm were obtained. The diffuse reflectance spectra were similar to the profile of a semiconductor material with the presence of thin transitions of Eu3+ in europium-doped K2NdNb5O15, as well as the transitions of Nd3+. The method of Kubelka-Munk was used for the estimation of bandgap energy. The values around 3.7 eV showed small variation with the concentration of Eu3+ ions in the K2NdNb5O15 host structure. The transitions were identified as direct ones type.

Modulated Phases and Domain Structure in Double Niobates With Tetragonal Tungsten Bronze - Like Structure

1982 ◽  
Vol 21 ◽  
Author(s):  
C. Manolikas
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
General Formula ◽  
Domain Structure ◽  
Room Temperature ◽  
Tungsten Bronze ◽  
Incommensurate Phase ◽  
Tetragonal Tungsten Bronze ◽  
Modulated Phases ◽  
Commensurate Phase

ABSTRACTThe domain structure and the commensurate - incommensurate transition of some niobates, with general formula A2BNb5O15 where A = Ba, Sr or Pb and B = Na or K, are examined by using electron microscopy and electron diffraction methods. A model of the commensurate phase at room temperature is proposed and the natureof the incommensurate phase is discussed.

Structure and electrical properties of tetragonal tungsten bronze Ba2CeFeNb4O15

RSC Advances ◽  
2015 ◽  
Vol 5 (94) ◽  
pp. 76957-76962 ◽  
Author(s):  
Hongqiang Ma ◽  
Kun Lin ◽  
Laijun Liu ◽  
Baoling Yang ◽  
Yangchun Rong ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electrical Property ◽  
Electrical Properties ◽  
Impedance Spectroscopy ◽  
Electron Diffraction ◽  
Tungsten Bronze ◽  
Ac Impedance Spectroscopy ◽  
Tetragonal Tungsten Bronze ◽  
X Ray ◽  
Selected Area Electron Diffraction

The crystal structure and electrical property of a tetragonal tungsten bronze ceramic, BaCeFeNb4O15, were investigated by synchrotron X-ray powder diffraction, selected area electron diffraction, and AC impedance spectroscopy.

Structural transition in KMnCrF6 – a chemically ordered magnetic ferroelectric

2015 ◽  
Vol 3 (17) ◽  
pp. 4321-4332 ◽  
Author(s):  
Christina Drathen ◽  
Takeshi Nakagawa ◽  
Wilson A. Crichton ◽  
Adrian H. Hill ◽  
Yasuo Ohishi ◽  
...  
Keyword(s):  
Room Temperature ◽  
Structural Transition ◽  
Tungsten Bronze ◽  
Orthorhombic Phase ◽  
Multiferroic Material ◽  
Tetragonal Tungsten Bronze

Emergence of an orthorhombic phase at room temperature suggests this tetragonal tungsten bronze fluoride to be a potential multiferroic material.

Sign in / Sign up

Export Citation Format

Share Document