Nanocrystalline powders of the lead-free piezoelectric

\r\nmaterial, tantalum-substituted potassium sodium niobate

\r\n(K0.5Na0.5)(Nb0.9Ta0.1)O3 (KNNT), were produced using a Retsch

\r\nPM100 planetary ball mill by setting the milling time to 15h, 20h,

\r\n25h, 30h, 35h and 40h, at a fixed speed of 250rpm. The average

\r\nparticle size of the milled powders was found to decrease from 12nm

\r\nto 3nm as the milling time increases from 15h to 25h, which is in

\r\nagreement with the existing theoretical model. An anomalous

\r\nincrease to 98nm and then a drop to 3nm in the particle size were

\r\nobserved as the milling time further increases to 30h and 40h

\r\nrespectively. Various sizes of these starting KNNT powders were

\r\nused to investigate the effect of milling time on the microstructure,

\r\ndielectric properties, phase transitions and piezoelectric properties of

\r\nthe resulting KNNT ceramics. The particle size of starting KNNT

\r\nwas somewhat proportional to the grain size. As the milling time

\r\nincreases from 15h to 25h, the resulting ceramics exhibit

\r\nenhancement in the values of relative density from 94.8% to 95.8%,

\r\nroom temperature dielectric constant (εRT) from 878 to 1213, and

\r\npiezoelectric charge coefficient (d33) from 108pC\/N to 128pC\/N. For

\r\nthis range of ceramic samples, grain size refinement suppresses the

\r\nmaximum dielectric constant (εmax), shifts the Curie temperature (Tc)

\r\nto a lower temperature and the orthorhombic-tetragonal phase

\r\ntransition (Tot) to a higher temperature. Further increase of milling

\r\ntime from 25h to 40h produces a gradual degradation in the values of

\r\nrelative density, εRT, and d33 of the resulting ceramics.<\/p>\r\n","references":null,"publisher":"World Academy of Science, Engineering and Technology","index":"Open Science Index 97, 2015"}