An Hardy - EMF 2015

Chemical solution synthesis and properties of nanoscale ferroelectrics, single phase
and composite multiferroics
An Hardy, and Marlies K. Van Bael
Hasselt University, Institute for Materials Research, Inorganic and Physical Chemistry and imec division
imomec, Martelarenlaan 42, 3500 Hasselt
*e-mail: [email protected]
Chemical solution syntheses are frequently used for the synthesis of many kinds of metal oxides. The cited
advantages include the compositional flexibility, high phase purity at relatively low temperatures, low
equipment and operation cost and for some cases, the compatibility with roll-to-roll processing. Here, we
focus on solution based synthesis of nanoscale BaTiO3 besides multiferroics.
First, the size limit for tetragonal BaTiO3 particles from solvothermal synthesis is investigated in view of
biomedical applications in SHRIMPs (Second Harmonic resonance Imaging Probe). Down to 50 nm, the
optimal nanocrystals produced strong SHG (second harmonic generation) signals, which is promising for
their use in cell imaging.
Second, solution-gel routes based on citrate complex precursors, are presented for the synthesis of
magnetoelectric multiferroic materials. Single phase BiFeO3 is the most studied multiferroic, showing both
ferroelectric and magnetic ordering at temperatures exceeding room temperature. The phase diagram
displays many different phases, complicating the synthesis of BiFeO3. Especially for chemical solution
deposited (CSD) thin films, limited knowledge is available. Therefore, we studied the phase formation and
stability of thin film BFO from aqueous CSD and found that the substrate, buffer layers and substituents
have a strong influence. Besides BFO, preliminary results on the hybrid improper ferroelectric, Ca3Mn2O7,
are reported. Finally, composite thin films of magnetic and ferroelectric phases are reported to show
enhanced magnetoelectric coupling through a high interface to volume ratio. Here, self-assembled
composite films are obtained via CSD. As high resolution TEM shows, composites are formed after
crystallizaton by phase separation between BaTiO3- or BiFeO3- CoFe2O4, resulting in highly textured films.
In conclusion, chemical solution synthesis provides easily accessible routes to nanoscale ferroelectrics and
multiferroic thin films, which hold great promise for diverse applications.
CV An Hardy,
An Hardy obtained a bachelor's and master's degree in chemistry (summa cum laude) from the
faculty of Sciences at Hasselt University (1998) and Ghent University (2000). She obtained a PhD
in chemistry at the laboratory of Inorganic and Physical Chemistry of Hasselt University in 2004, as
a PhD fellow of the Research Foundation Flanders (FWO Vlaanderen), specializing in the aqueous
solution synthesis and deposition of ferroelectric lanthanum substituted bismuth titanate. She
continued her work on the chemical synthesis of oxides as a postdoctoral fellow of the FWO in the
same research group, whilst taking up a position as a lecturer in the department of Applied
Engineering at XIOS University College, associated to Hasselt University.
In 2009 she was appointed as assistant professor and since 2012 as associate professor at Hasselt
University, and takes charge of the group of Inorganic and Physical Chemistry together with full
professor Dr. Marlies K. Van Bael. The group currently consists of 2 professors, 3 postdoctoral
researchers, and 15 PhD students. The research has been presented at various international
conferences in about 20 invited talks in national and international colloquia and published in more
than 70 papers in international papers with over 700 citations.
The group has expertise in chemical solution based synthesis (sol-gel, precipitation, hydrothermal)
and deposition of nanostructured inorganic materials (particles, layers), and characterization
methods required for understanding precursor – final oxide transformations (Thermal analysis,
EXAFS, XRD, SEM, TEM, UV-Raman, FTIR, etc.). Materials that are investigated include
conductive and semiconductive oxides, dielectrics, ferroelectrics, multiferroics, LIB cathode
materials, etc. where added value is created by the use of solution processing.