41 research outputs found
Mechanism of the Phase Change in PbK2LiNb5O15: Dielectric, structural, and Raman scattering studies
Experiments reveal that PbK2LiNb5O15 which belongs to the tetragonal tungsten
bronze family presents paraelectric and ferroelectric phases and a complex
structural change between them. High and low temperature phases are of symmetry
P4/mbm and Pba2 respectively, so that this change is also of ferroelastic type.
As presented here, crystallographic results hint at a displacive character of
the ferroelectric ordering but show a more complex behaviour, with a clear
order-disorder mechanism which accompanies the appearance of ferroelasticity.
To complete our knowledge of this material, we have performed Raman experiments
which exhibit a low frequency mode, but no clear soft mode is observed
MECHANISM OF THE PHASE CHANGE IN PbK2LiNb5O15: Dielectric, structural, and Raman scattering studies
Experiments reveal that PbK2LiNb5O15 which belongs to the tetragonal tungsten bronze family presents paraelectric and ferroelectric phases and a complex structural change between them. High and low temperature phases are of symmetry P4/mbm and Pba2 respectively, so that this change is also of ferroelastic type. As presented here, crystallographic results hint at a displacive character of the ferroelectric ordering but show a more complex behaviour, with a clear order-disorder mechanism which accompanies the appearance of ferroelasticity. To complete our knowledge of this material, we have performed Raman experiments which exhibit a low frequency mode, but no clear soft mode is observed
Effect of the BaO-NaO-NbO-PO glass addition on microstructure and dielectric properties of BNN ceramics
Barium sodium niobate BaNaNbO (BNN) ceramics with different
amounts of BaO-NaO-NbO-PO (BNNP) glass were prepared via
the conventional solid-state method. The effect of glass content on the
structural, microstructure, and dielectric properties of BNN ceramics was
investigated. The XRD results showed that no secondary phase was formed after
adding BNNP glass. It was found that such additions reduce the average grain
size and refine the microstructure of the obtained ceramics. Moreover, the
samples exhibited a stable dielectric constant over the temperature range of
25C-150C, and their dielectric constants were significantly
improved. The ceramic with 7.5 wt% BNNP glass content showed a dielectric
constant which is more than twice as much as that of pure BNN ceramic, as well
as a low dielectric loss of less than 5%.Comment: 5 pages, 5 figure
Enhanced RCP and large inverse magnetocaloric effect of CoFeO nanoparticles synthesized by auto-combustion method
This work focuses on the microstructure, magnetic properties and
magnetocaloric effect of CoFeO (CFO) nanoparticles elaborated by
sol-gel auto combustion method. The XRD investigation indicates that CFO is
crystallized in a cubic spinel structure and the SEM micrograph shows a fine
quasi-spherical with an average grain sizes of 160 nm. The temperature
dependence of the Raman spectra reveals the ferromagnetic to paramagnetic
(FM-PM) transition started from 723 K and the magnetization versus temperature
measurements shows the Curie temperature located at T = 785 K. Large
value of magnetocaloric temperature change of T =11.2 K with a high RCP
of 687.56 J Kg are achieved indirectly via the Maxwell approach making
our CFO nanopowder suitable candidate for both environmentally friendly
magnetic refrigeration and medical applications at ambient temperature
Room-temperature magnetoelectric effect in lead-free multiferroic BaCaTiSnO-CoFeO particulate composites
Multiferroic particulate composites
BaCaTiSnO-CoFeO with (
= 0.1, 0.2, 0.3, 0.4 and 0.5) have been prepared by mechanical mixing of the
calcined and milled individual ferroic phases. X-ray diffraction and Raman
spectroscopy analysis confirmed the formation of both perovskite
BaCaTiSnO (BCTSn) and spinel
CoFeO (CFO) phases without the presence of additional phases. The
morphological properties of the composites were provided by using Field
Emission Scanning Electron Microscopy. The BCTSn-CFO composites exhibit
multiferroic behavior at room temperature, as evidenced by ferroelectric and
ferromagnetic hysteresis loops. The magnetoelectric (ME) coupling was measured
under a magnetic field up to 10 kOe and the maximum ME response found to be 0.1
mV /cm/ Oe for the composition 0.7 BCTSn-0.3 CFO exhibiting a high degree of
pseudo-cubicity and large density
Raman response of quantum critical ferroelectric pb-doped srtio3
A quantum paraelectric SrTiO3 is a material situated in close proximity to a quantum critical point (QCP) of ferroelectric transition in which the critical temperature to the ferroelectric state is suppressed down to 0 K. However, the understanding of the behavior of the phase transition in the vicinity of this point remains challenging. Using the concentration x of Pb in solid solution Sr1−x Pbx TiO3 (PSTx) as a tuning parameter and applying the combination of Raman and dielectric spectroscopy methods, we approach the QCP in PSTx and study the interplay of classical and quantum phenomena in the region of criticality. We obtain the critical temperature of PSTx and the evolution of the temperature-dependent dynamical properties of the system as a function of x to reveal the mechanism of the transition. We show that the ferroelectric transition occurs gradually through the emergence of the polar nanoregions inside the non-polar tetragonal phase with their further expansion on cooling. We also study the ferroelastic cubic-to-tetragonal structural transition, occurring at higher temperatures, and show that its properties are almost concentration-independent and not affected by the quantum criticality.Fil: Linnik, Ekaterina D.. Southern Federal University; RusiaFil: Mikheykin, Alexey S.. Southern Federal University; RusiaFil: Rubi, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes; ArgentinaFil: Shirokov, Vladimir B.. No especifíca;Fil: Mezzane, Daoud. No especifíca;Fil: Kondovych, Svitlana V.. No especifíca;Fil: Lukyanchuk, Igor A.. No especifíca;Fil: Razumnaya, Anna G.. Southern Federal University; Rusi
Structural, dielectric and electrocaloric properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3 ceramics elaborated by sol-gel method
Ferroelectric ceramics (Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3 (x=0.00, 0.02, 0.04,
0.06) were prepared by a sol-gel method. Structural investigation revealed the
co-existence of tetragonal (P4mm) and orthorhombic (Pmm2) symmetries at room
temperature for the undoped ceramic, while only a tetragonal structure (P4mm)
was observed for the doped ceramics. Dielectric measurements indicate a
dielectric relaxation process at high temperatures which is essentially related
to the hopping of oxygen vacancies. Furthermore, a down shifting of the Curie
temperature (TC) with increasing Sn4+ doping rate has been revealed. The
temperature profiles of the Raman spectra unveiled the existence of polar
nanoregions (PNRs) above the Curie temperature in all ceramics. The
ferroelectric properties were found to be related to the microstructure.
Electrocaloric effect was investigated in this system that revealed an
electrocaloric responsivity of 0.225 10-6 K m/V for the composition with x =
0.04 Sn doping, where other remarkable physical properties were also observed
Electrocaloric effect and high energy storage efficiency in lead-free BaCaTiSnO ceramic elaborated by sol-gel method
Structural, dielectric, ferroelectric, energy storage properties, and
electrocaloric effect were studied in lead-free ceramic
BaCaTiSnO (BCTSn) elaborated by sol-gel
method. Phase purity structure was confirmed from X-ray data using Rietveld
refinement analysis which revealed the coexistence of tetragonal (P4mm) and
orthorhombic (Amm2) symmetries at room temperature. Phase transitions were
detected by dielectric and differential scanning calorimetry results. Energy
storage properties were determined from P-E hysteresis, and the electrocaloric
properties were calculated indirectly via the Maxwell approach. The large value
of electrocaloric temperature change of T=0.807 K obtained at a
relatively small field of 30 kV cm and high energy storage efficiency
can make BCTSn ceramic a promising candidate for environmentally friendly
refrigeration and energy storage applications