Microstructure and piezoelectric properties of (Na0.5K0.5)NbO3 lead-free piezoelectric ceramics with V2O5 addition

Various amounts of Nb
₂
O
₅
in the (Na
_0.5
K
_0.5
) NbO
₃
(NKN) ceramic were replaced by V
₂
O
₅
to decrease its sintering temperature to below 950°C. A small V
₂
O
₅
content resulted in a dense microstructure with an increased grain size for the specimen sintered at 900°C due to the presence of a liquid phase. When V
₂
O
₅
was added to the NKN ceramics, their orthorhombic-to-tetragonal transition temperature increased from 178°C to around 200°C. However, their Curie temperature decreased from 402°C to around 330°C. The k
_p
,
_ε3

^T
/
_ε0
, and Q
_m
values increased with V
₂
O
₅
addition, probably due to the increased density and poling state, which was identified by the phase angle. The specimen with x = 0.05, sintered at 900°C for 8 h, exhibited the following piezoelectric properties: k
_p
= 0.32,
_ε3

^T
/
_ε0
= 245, d
₃₃
= 120 (pC/N), and Q
_m
= 232.