Research
Exploaring Novel Mixed Anion Materials
Metal oxides represent one of the largest groups of compounds within ceramic
materials. Because oxygen is abundant in the atmosphere, most metal oxides
can be readily synthesized by simply heating metal-containing precursors
in air. Over the years, a wide variety of metal oxides have been developed
by varying the composition of metal ions.
In our laboratory, we focus not only on the composition of metal cations
but also on the anionic components, aiming to synthesize new materials.
In addition to oxide ions, ceramic materials can incorporate other anions
such as nitride ions, halides, and molecular anions like nitrate. Compounds
containing multiple types of anions are referred to as mixed-anion compounds,
and they are attracting attention as materials that expand the conventional
concept of metal oxides.
Our research particularly emphasizes the synthesis of new mixed-anion compounds
and ceramic materials based on oxyfluorides—compounds that combine oxygen
and fluorine anions.
Negative Thermal Expansion
Most materials expand in heating—a phenomenon known as thermal expansion.
However, some compounds exhibit the unusual behavior of contracting upon
heating. This phenomenon, characterized by a negative coefficient of thermal
expansion, is referred to as negative thermal expansion (NTE).
In recent years, materials exhibiting large NTE have been discovered by
utilizing phase transitions accompanied by volume contraction. Our laboratory
focuses on compounds that undergo such volume-shrinking phase transitions,
and we aim to discover new NTE materials by controlling their chemical
composition.
Dielectric Materials
Insulating materials that do not conduct electricity can store electric
charge when a voltage is applied. This property is known as dielectric
behavior and is widely utilized in electronic components such as capacitors.
For ceramic materials to exhibit dielectric properties, the geometric arrangement
of positively charged cations and negatively charged anions within the
crystal structure plays a crucial role.
Our laboratory focuses on this structural aspect, aiming to synthesize
new dielectric materials by combining elements with different valence states.
Magnetic Materials
Magnetism is also one of the key functionalities of ceramic materials.
Compounds containing magnetic ions with unpaired electrons can exhibit
magnetic properties, but to realize these functionalities, it is essential
to control the macroscopic magnetic ordering.
Magnetic ordering is governed by critical parameters such as the electronic
state of unpaired electrons within magnetic ions and the interactions between
those ions.
Our laboratory investigates materials that exhibit unique magnetic properties
by introducing mixed-anion configurations—an approach that enables magnetic
behaviors unattainable in single-anion compounds.
Crystal Structure Analysis via Diffraction Methods
Investigation of ceramic materials requires a clear grasp of their atomic
structure. Without knowing how atoms are arranged, it is impossible to
meaningfully discuss material properties. Among the various techniques
available, diffraction methods are among the most powerful tools for elucidating
the crystal structures of ceramics.
In our laboratory, we conduct experiments using X-rays and synchrotron
radiation at external research facilities to precisely evaluate the crystal
structures of synthesized compounds.