MATERIAŁY ELEKTRONICZNE - ITME

K. Orliński
MULTIFUNCIONALITY OF MULTIFERROIC-BASED
EUTECTIC COMPOSITES
Krzysztof Orliński
Institue of Electronic Materials Technology, ul. Wólczyńska 133, 01-919 Warszawa
e-mail: krzysztof.orlinski@itme.edu.pl
Present work is dedicated to functional description of eutectic
composites containing rare earth ferrite – REFeO 3
. Materials
that fall under this cathegory exhibit spontaneous dielectric
and magnetic polarization – they behave as ferroelectrics
and ferromagnets and can be “tuned” by small additions of
other rare earth elements without causing large crystal lattice
distortions. Special attention was payed to multifunctionality
that, in majority, comes from the control of the structural refinement
with the supercooling of the crystallizing liquid.
Key words: composite, eutectic, multiferroic, ferromagnetism,
ferroelectric, perovskite, catalyst, green, energy
„Wielofunkcjonalność w kompozytach
eutektycznych na osnowie multiferroicznej”
Niniejsza praca poświęcona jest opisowi funkcjonalności
eutektycznych kompozytów na osnowie ferrytów metali ziem
rzadkich – REFeO 3
. Materiały należące do tej grupy wykazują
jednocześnie spontaniczną polaryzację dielektryczną
(ferroelektryczność) i magnetyczną (ferromagnetyzm) a ponadto
dają się „stroić” za pomocą domieszek innych metali
ziem rzadkich nie powodując silnych zniekształceń sieci
krystalicznej. Szczególną uwagę zwrócono na wielofunkcjonalność
wynikającą w dużej mierze z możliwości sterowania
rozdrobnieniem struktury za pomocą zmiany przechłodzenia
krystalizującej cieczy.
słowa kluczowe: kompozyt, eutektyka, multiferroik, ferromagnetyzm,
ferroelektryczność, perowskit, katalizator,
energia, zielona
1. INTRODUCTION
During recent years we witnessed emerging of
a variety of faster and more efficient optoelectronic
and photonic elements. The introduction of optical
fibres was but one of those improvements that made
information transfer faster and more efficient. The
next step, leading to substitution of electricity with
light is far more complex and cannot be achieved
without special materials. As photons are quanta of
electromagnetic waves, both: electric and magnetic
force is needed to influence their trajectory. A branch
of photonic composite materials called metamaterials
is dedicated to demonstration of special properties,
not found in nature, such as negative refraction [1
- 2] or invisibility in certain wavelength spectrum
– “cloaking” [3 - 4].
Moreover, along with the technology standards,
the needs for energy have grown and we found ourselves
in necessity of finding its novel sources, as
well as increasing the efficiency of existing ones. As
the production of large amounts of energy, usually
follows the release of greenhouse gases: carbon,
nitrogen and sulfur oxides, the demand for better
low-cost catalysts of combustion processes is very
high as well. Thus, along with materials for low-cost
catalysis 5 much effort is being put into green energy
sources (solid oxide fuel cells [6 - 8] , photovoltaics)
and environmental monitoring (chemical sensing
[9 - 10], air purification [11 - 12]).
To rise to that challenge, the materials of 21 st
century should possess all, or at least most of those
properties. I would like to focus on how to achieve
such multifunctionality by using simple rules of
material science and physics. Such distinct set of
properties was found in a group of materials called
multiferroics.
2. MULTIFERROICS
Materials, which exhibit both: ferroelectric and
ferromagnetic behaviour are called multiferroics.
Those materials crystallize typically in two types
of structures: perovskite and spinel. The spinel
structure, although described by cubic symmetry, is
very complex and as such, will not be the subject
of further discussion. Instead, the crystal group of
perovskite compounds shall be introduced.
The amount of charge stored inside the material
is highly dependent on the dielectric permittivity and
is found to be the highest in a group called ferroelectrics.
Similarly to ferromagnetics, these materials
show spontaneous polarization of dipoles in certain
direction. Oxide perovskites (Fig. 1) are materials
which very often exhibit ferroelectric behaviour.
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