Department;
of;
Physics;
and;
Materials;
Science,;
City;
University;
of;
Hong;
Kong,;
Hong;
Kong,;
China;
Shanghai;
Institute;
of;
Ceramics,;
Chinese;
Academy;
of;
Sciences,;
Shanghai;
200050,;
China;
College;
of;
Materials;
Science;
and;
Engineering,;
Hunan;
University,;
Changsha;
410082,;
China;