scholarly journals Dielectric investigations of La-doped barium titanate

2010 ◽  
Vol 4 (3) ◽  
pp. 193-198 ◽  
Author(s):  
Tadas Ramoska ◽  
Juras Banys ◽  
Ricardas Sobiestianskas ◽  
Mirjana Vijatovic-Petrovic ◽  
Jelena Bobic ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Barium Titanate ◽  
High Frequency ◽  
Low Frequency ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Relaxational Process ◽  
Pechini Process ◽  
La Doped ◽  
Curie Temperature Tc

In the present paper results of the dielectric investigation of barium titanate (BaTiO3) doped with different concentrations of lanthanum are presented. Ceramic samples were prepared by the Pechini process. With increased doping the grain size of ceramics decreases from 2.5 ?m in pure samples down to 0.2 ?m in 0.5 mol% La - doped BaTiO3. Ceramics showed maximally enhanced dielectric permittivity around low-, room and high temperature phase transitions, which are the phase transitions of the pure BaTiO3. The Curie temperature, TC, is lowered by 30 K with increase of doping concentration to 0.5 mol% La. Dielectric spectra revealed three parts: low frequency part which is caused by conductivity process, middle frequency relaxational process part and high frequency relaxational/polar modes contribution.

High temperature phase transitions and proton conductivity in some kdp-family crystals

1989 ◽  
Vol 100 (1) ◽  
pp. 135-141 ◽  
Author(s):  
A. I. Baranov ◽  
V. P. Khiznichenko ◽  
L. A. Shuvalov
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Proton Conductivity ◽  
High Temperature Phase ◽  
Temperature Phase

scholarly journals High-temperature phase transitions in dense germanium

2021 ◽  
Vol 154 (17) ◽  
pp. 174702
Author(s):  
Liam C. Kelsall ◽  
Miriam Peña-Alvarez ◽  
Miguel Martinez-Canales ◽  
Jack Binns ◽  
Chris J. Pickard ◽  
...  
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase

High-temperature phase transitions in K3H(SO4)2

2001 ◽  
Vol 145 (1-4) ◽  
pp. 179-184 ◽  
Author(s):  
Calum R.I. Chisholm ◽  
Sossina M. Haile
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase

High-temperature phase transitions in the improper ferroelectric KIO3

2008 ◽  
Vol 81 (1) ◽  
pp. 29-41 ◽  
Author(s):  
M. M. Abdel-Kader ◽  
F. El-Kabbany ◽  
H. Naguib ◽  
W. M. Gamal
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase

scholarly journals Investigations of High Temperature Phase Transitions in (NH3c2H5)2CuCl4Crystals

1999 ◽  
Vol 95 (3) ◽  
pp. 351-357 ◽  
Author(s):  
V. Kapustianik ◽  
Yu. Korchak ◽  
S. Sveleba ◽  
R. Tchukvinskyi ◽  
I. Girnyk
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase

scholarly journals Phase Transitions in Borohydride Perovskites

2014 ◽  
Vol 70 (a1) ◽  
pp. C73-C73
Author(s):  
Pascal Schouwink ◽  
Radovan Cerny
Keyword(s):  
Phase Transitions ◽  
Volume Expansion ◽  
Host Lattice ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
New Class ◽  
Structural Distortions ◽  
Complex Hydrides ◽  
Type Lattice

A series of complex hydrides based on the highly dynamic tetrahydroborate anion BH4-and crystallizing in theABX3type lattice has recently been discovered. They present a rare case of a family of iono-covalent hydrides that has a genuine tunable host lattice, making them an interesting new class of host compounds for not only the design of hydrogen storage materials but also hydride-properties related to heavy metals. Amongst these, preliminary results onREE-based luminescence will be discussed in the neat and doped compounds, the Ln2+excited states surprisingly not being subject to significant quenching by B-H vibrations. Unlike oxide- or halide-perovskites some members of theAB(BH4)3group do not evolve to higher symmetries as a function of temperature. We show by means ofin-situsynchrotron X-ray powder diffraction, vibrational spectroscopy andab initiocalculations in the solid state, that temperature-induced structural distortions in perovskite-typeACa(BH4)3(A= K, Rb, Cs) have their origin in close hydridic di-hydrogen contacts of repulsive nature. Coupling between internal B-H vibrations and phonons results in lattice distortions that are identical in symmetry to well-known instabilities (soft modes) in perovskites, which generally condense to lower temperatures. Anion-substitution BH4-<->X-(X= Halide) calculated on ordered models can relax distortions caused by repulsive effects. High temperature phase-transitions inACa(BH4)3can be of first or second-order, including 2-fold superlattices, simple cubic-cubic transitions accompanied by volume expansion or complex modulated superstructures accompanied by negative volume expansion, as is the case in RbCa(BH4)3. Close di-hydrogen contacts may be suggested as a tool to tailor the crystal symmetry in complex hydride perovskites in the future.

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