, on the restriction of the use of certain hazardous substances in electrical and electronic equipment, Off, EC of the European Parliament, pp.46-65, 2002.

Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori et al., Lead-free piezoceramics, Nature, vol.36, issue.Suppl. Iss., pp.84-87, 2014.
DOI : 10.1143/JJAP.36.5963

F. Rubio-marcos, J. J. Romero, J. F. Fernández, and P. Marchet, Control of the crystalline structure and piezoelectric properties of)O3 ceramics through transition metal oxide doping, Appl. Phys. Express, vol.4, 2011.
URL : https://hal.archives-ouvertes.fr/hal-00659579

G. Lévêque, P. Marchet, F. Levassort, L. P. Tran-huu-hue, J. R. Duclere et al., )O3 piezoelectric ceramics: influence of sintering atmosphere and ZrO2 doping on densification, microstructure and piezoelectric properties, J. Eur. Ceram. Soc, pp.31-577, 2011.

M. Bah, F. Giovannelli, F. Schoenstein, C. Brosseau, and J. ,

E. Haumesser, I. Le-clezio, and . Monot-laffez, Ultrasonic transducers based on undoped leadfree (K0.5Na0.5)NbO3 ceramics, Ultrasonics, pp.63-86, 2015.
URL : https://hal.archives-ouvertes.fr/hal-01627834

J. Taub, L. Ramajo, and M. S. Castro, Phase structure and piezoelectric properties of Ca- and Ba-doped K1/2Na1/2NbO3 lead-free ceramics, Ceramics International, vol.39, issue.4, pp.39-3555, 2013.
DOI : 10.1016/j.ceramint.2012.10.181

B. Malic, J. Bernard, J. Holc, D. Jenko, and M. Kosec, Alkaline-earth doping in (K,Na)NbO3 based piezoceramics, Journal of the European Ceramic Society, vol.25, issue.12, pp.25-2707, 2005.
DOI : 10.1016/j.jeurceramsoc.2005.03.127

X. Vendrell, J. E. García, X. Bril, D. A. Ochoa, L. Mestres et al., Improving the functional properties of (K0.5Na0.5)NbO3 piezoceramics by acceptor doping, Journal of the European Ceramic Society, vol.35, issue.1
DOI : 10.1016/j.jeurceramsoc.2014.08.033

URL : https://hal.archives-ouvertes.fr/hal-01116307

. Soc, , pp.125-130, 2015.

G. Zang, X. Yi, J. Du, and Y. Wang,

. Lett, , pp.1394-1397, 2010.

D. Lin, D. Huang, and Q. , Structure, dielectric and piezoelectric properties of K0.5Na0.5NbO3???Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 ceramics, Journal of Physics and Chemistry of Solids, vol.74, issue.7, pp.1021-1025, 2013.
DOI : 10.1016/j.jpcs.2013.02.023

F. Li, D. Xiao, J. Wu, Z. Wang, C. Liu et al., Phase structure and electrical properties of (K0.5Na0.5)NbO3???(Bi0.5Na0.5)ZrO3 lead-free ceramics with a sintering aid of ZnO, Ceramics International, vol.40, issue.9, pp.14601-14605, 2014.
DOI : 10.1016/j.ceramint.2014.06.045

X. P. Jiang, Y. Chen, K. H. Lam, S. H. Choy, and J. Wang, Effects of MnO doping on properties of 0.97K0.5Na0.5NbO3???0.03(Bi0.5K0.5)TiO3 piezoelectric ceramics, Journal of Alloys and Compounds, vol.506, issue.1, pp.323-326, 2010.
DOI : 10.1016/j.jallcom.2010.06.200

X. Li, M. Jiang, J. Liu, J. Zhu, X. Zhu et al., Lead-Free Ceramics, Journal of the American Ceramic Society, vol.92, issue.7, pp.1625-1628, 2009.
DOI : 10.1111/j.1551-2916.2009.03090.x

URL : https://hal.archives-ouvertes.fr/hal-01486596

T. M. Harkulich, J. Magder, M. S. Vukasovich, and R. J. Lockhart, Ferroelectrics of Ultrafine Particle Size: II, Grain Growth Inhibition Studies, Journal of the American Ceramic Society, vol.42, issue.6, 1966.
DOI : 10.1111/j.1151-2916.1966.tb13266.x

M. Bah, F. Giovannelli, F. Schoenstein, G. Feuillard, E. Le-clezio et al., Monot-Laffez, High electromechanical performance with spark plasma sintering of undoped K0.5Na0.5NbO3 ceramics, Ceram. Int, vol.40, 2014.
DOI : 10.1016/j.ceramint.2013.12.097

D. Lin, K. W. Kwok, and H. L. Chan, Phase structures and electrical properties of K0.5Na0.5(Nb0.925Ta0.075)O3?LiSbO3 lead-free piezoelectric ceramics, J. Phys. D: Appl. Phys, vol.4040, pp.6060-6070, 2007.

J. Wu, T. Peng, Y. Wang, D. Xiao, J. Zhu et al., Phase Structure and Electrical Properties of (K0.48Na0.52)(Nb0.95Ta0.05)O3-LiSbO3 Lead-Free Piezoelectric Ceramics, Journal of the American Ceramic Society, vol.90, issue.[5], pp.319-321, 2008.
DOI : 10.1111/j.1551-2916.2007.02102.x

S. Qian, K. Zhu, X. Pang, J. Liu, J. Qiu et al., Phase transition, microstructure, and dielectric properties of Li/Ta/Sb co-doped (K, Na)NbO3 lead-free ceramics, Ceramics International, vol.40, issue.3, pp.4389-4394, 2014.
DOI : 10.1016/j.ceramint.2013.08.110

F. Rubio-marcos, P. Marchet, T. Merle-méjean, and J. F. Fernandez, Role of sintering time, crystalline phases and symmetry in the piezoelectric properties of lead-free KNNmodified ceramics, Mater. Chem. Phys, pp.123-91, 2010.
URL : https://hal.archives-ouvertes.fr/hal-00496783

J. Zhou, J. Li, K. Wang, and X. Zhang, Phase structure and electrical properties of (Li,Ta)-doped (K,Na)NbO3 lead-free piezoceramics in the vicinity of Na/K??=??50/50, Journal of Materials Science, vol.102, issue.15
DOI : 10.1063/1.2752799

. Mater and . Sci, , pp.5111-5116, 2011.

Y. Zhen and J. Li, -Based Ceramics: Influence of Sintering Temperature on Densification, Microstructure, and Electrical Properties, Journal of the American Ceramic Society, vol.87, issue.9
DOI : 10.1111/j.1551-2916.2006.00960.x

. Soc, , pp.3669-3675, 2006.

E. Hollenstein, M. Davis, D. Damjanovic, and N. Setter, Piezoelectric properties of Li-and Tamodified (K0.5Na0.5)NbO3 ceramics, Appl. Phys. Lett, vol.87, 2005.

H. Li, W. Yang, Y. Li, Q. Meng, and Z. Zhou, Room-temperature magnetocapacitance in Fedoped K0, Appl. Phys. Express, vol.5

B. Zhang, J. Wu, X. Wang, X. Cheng, J. Zhu et al., Rhombohedral???orthorhombic phase coexistence and electrical properties of Ta and BaZrO3 co-modified (K, Na)NbO3 lead-free ceramics, Current Applied Physics, vol.13, issue.8, pp.1647-1650, 2013.
DOI : 10.1016/j.cap.2013.06.010

S. Y. Lee, C. W. Ahn, J. S. Kim, A. Ullah, H. J. Lee et al., Enhanced piezoelectric properties of Ta substituted-(K0.5Na0.5)NbO3 films: A candidate for lead-free piezoelectric thin films, Journal of Alloys and Compounds, vol.509, issue.20, pp.194-198, 2011.
DOI : 10.1016/j.jallcom.2011.03.031

S. Y. Lee, J. S. Kim, C. W. Ahn, A. Ullah, H. J. Lee et al., Influence of piezoelectric property on annealing temperature of Ta-substituted (K0.5Na0.5)NbO3 thin films by chemical solution deposition, Current Applied Physics, pp.11-157, 2011.
DOI : 10.1016/j.cap.2011.01.032

L. Zheng, X. Huo, R. Wang, J. Wang, W. Jiang et al., Large size lead-free (Na,K)(Nb,Ta)O3 piezoelectric single crystal: growth and full tensor properties, CrystEngComm, vol.350, issue.38, pp.15-7718, 2013.
DOI : 10.4028/www.scientific.net/KEM.350.85

T. Hattori, Y. Kitanaka, Y. Noguchi, and M. Miyayama, Growth and ferroelectric/piezoelectric properties of (K,Na)(Nb,Ta)O3 ferroelectric single crystals, Key Eng. Mater, vol.566, 2013.

M. Bah, F. Giovannelli, R. Retoux, J. Bustillo, E. L. Clezio et al., by the Floating Zone Method, Crystal Growth & Design, vol.16, issue.1, pp.315-324, 2016.
DOI : 10.1021/acs.cgd.5b01271

URL : https://hal.archives-ouvertes.fr/hal-01255208

L. Chen, G. Qiu, B. Peng, M. Guo, and M. Zhang, (K0.5Na0.5)(Nb1???xTax)O3 ceramics with a higher d33: Preparation from a two-stage microwave hydrothermal process, Ceramics International, vol.41, issue.10, pp.13331-13340, 2015.
DOI : 10.1016/j.ceramint.2015.07.117

URL : https://hal.archives-ouvertes.fr/in2p3-00169733

A. Hussain, A. Maqbool, J. S. Kim, T. K. Song, M. H. Kim et al., Ceramics Prepared by Reactive Template Grain Growth Method, International Journal of Applied Ceramic Technology, vol.25, issue.8, pp.228-234, 2015.
DOI : 10.1016/j.jeurceramsoc.2005.03.127

Y. G. Lv, C. L. Wang, J. L. Zhang, L. Wu, M. L. Zhao et al., Tantalum influence on physical properties of (K0.5Na0.5)(Nb1?xTax)O3 ceramics, pp.44-284, 2009.

M. Matsubara, K. Kikuta, and S. Hirano, Piezoelectric properties of (K0.5Na0.5)(Nb1???xTax)O3???K5.4CuTa10O29 ceramics, Journal of Applied Physics, vol.37, issue.11, 2005.
DOI : 10.1080/00150198908017369

M. Matsubara, T. Yamaguchi, W. Sakamoto, K. Kikuta, T. Yogo et al., Processing and Piezoelectric Properties of Lead-Free (K,Na) (Nb,Ta) O3 Ceramics, Journal of the American Ceramic Society, vol.6, issue.8, pp.1190-1196, 2005.
DOI : 10.1103/PhysRev.114.63

J. Zhou, L. Cheng, K. Wang, X. Zhang, J. Li et al., Fang, Low-temperature sintering of (K,Na)NbO3-based lead-free piezoceramics with addition of LiF, J. Eur. Ceram

. Soc, , pp.1161-1167, 2014.

Y. Watanabe, K. Sumida, S. Yamada, S. Sago, S. Hirano et al., Effect of Mn-doping on the piezoelectric properties of (K0.5Na0.5)(Nb0.67Ta0.33)O3 lead-free ceramics

, Phys, vol.47, pp.3556-3558, 2008.

R. E. Jaeger and L. Egerton, Hot Pressing of Potassium-Sodium Niobates, Journal of the American Ceramic Society, vol.43, issue.10, pp.209-213, 1962.
DOI : 10.1111/j.1151-2916.1962.tb11127.x

G. Corapcioglu, M. A. Gulgun, K. Kisslinger, S. Sturm, S. K. Jha et al., Microstructure and microchemistry of flash sintered K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub>, Journal of the Ceramic Society of Japan, vol.124, issue.4, pp.321-328, 2016.
DOI : 10.2109/jcersj2.15290

J. Li, K. Wang, B. Zhang, and L. Zhang, Ferroelectric and Piezoelectric Properties of Fine-Grained Na0.5K0.5NbO3 Lead-Free Piezoelectric Ceramics Prepared by Spark Plasma Sintering, Journal of the American Ceramic Society, vol.87, issue.2, pp.706-709, 2006.
DOI : 10.1111/j.1551-2916.2004.01477.x

F. Delorme, M. Bah, F. Schoenstein, F. Jean, and M. Z. Jabli,

. Giovannelli, Thermoelectric properties of oxygen deficient (K0.5Na0.5)NbO3 ceramics, Mater. Lett, vol.162, pp.24-27, 2016.
URL : https://hal.archives-ouvertes.fr/hal-01755969

J. Rodriguez, Recent advances in magnetic structure determination by neutron powder diffraction, Physica B: Condensed Matter, vol.192, issue.1-2, pp.55-69, 1993.
DOI : 10.1016/0921-4526(93)90108-I

, IEEE Standard 176 -1987, IEEE Standard on Piezoelectricity, 1987.

N. Ishizawa, J. Wang, T. Sakakura, Y. Inagaki, and K. Kakimoto, Structural evolution of Na0.5K0.5NbO3 at high temperatures, Journal of Solid State Chemistry, vol.183, issue.11, pp.2731-2738, 2010.
DOI : 10.1016/j.jssc.2010.09.018

, JCPDS reference, pp.4-017, 2014.

H. E. Mgbemere, M. Hinterstein, and G. A. Schneider, Structural phase transitions and electrical properties of (KxNa1???x)NbO3-based ceramics modified with Mn, Journal of the European Ceramic Society, vol.32, issue.16
DOI : 10.1016/j.jeurceramsoc.2012.07.033

, Soc, vol.32, pp.4341-4352, 2012.

P. Mahesh, D. Pamu, and . Raman, Dielectric Studies on Lead free (K0.5Na0.5)NbO3 Piezoelectric Ceramics, IOP Conference Series: Materials Science and Engineering, pp.73-012141, 2015.

W. Zhu, J. Zhu, M. Wang, B. Zhu, X. Zhu et al., lead-free ceramics and its application to study grain/domain orientation, Journal of Raman Spectroscopy, vol.87, issue.9, p.1320, 2012.
DOI : 10.1007/s00340-007-2589-7

C. W. Ahn, H. J. Seog, A. Ullah, S. Y. Lee, J. W. Kim et al., Effect of Ta content on the phase transition and piezoelectric properties of lead-free (K0, )O3 thin film, J. App. Phys, pp.111-024110, 2012.

M. Polomska, B. Hilczer, M. Kosec, and B. Malic, Raman scattering dtudies of lead free (1- x)K0.5Na0.5NbO3-xSrTiO3 relaxors, Ferroelectrics, vol.369, issue.149, 2008.

M. Mirza, T. Shamim, K. Ishidate, and . Ohi, High pressure Raman study of KNbO3-KTaO3 and KNbO3-NaNbO3 mixed crystals, J. Phys. Soc. Jp, vol.72, p.551, 2003.

X. Vendrell, J. E. Garcia, E. Cerdeiras, D. A. Ochoa, F. Rubio-marcos et al.,

. Mestres, Effect of lanthanide doping on structural, microstructural and functional properties of K0.5Na0.5NbO3 lead-free piezoceramics, Ceramics International, pp.42-17530, 2016.

J. Wang and L. Luo, The NbO6 octahedral distortion and phase structural transition of Eu3+- doped K0.5Na0.5NbO3-xLiNbO3 ferroelectric ceramics, J. Am. Ceram. Soc, vol.1, 2017.
DOI : 10.1111/jace.15180

URL : http://onlinelibrary.wiley.com/doi/10.1111/jace.15180/pdf

S. Glin?ek, D. Nuzhnyy, J. Petzelt, B. Mali?, S. Kamba et al., ceramics, Journal of Applied Physics, vol.24, issue.10, 2012.
DOI : 10.1088/0953-8984/3/21/003

C. H. Perry and T. F. Mcnelly, Physical Review, vol.23, issue.2, p.456, 1967.
DOI : 10.1016/0022-3697(62)90084-7

J. Kreisel, A. M. Glazer, P. Bouvier, and G. Lucazeau, High pressure Raman study of a relaxor ferroelectric: The Na0.5Bi0.5TiO3 perovskite, Phys. Rev. B, vol.63, 2001.
URL : https://hal.archives-ouvertes.fr/hal-01685107

, Soft-mode spectroscopy in Fe:KTa1- xNbxO3 crystals, Cryst. Res. Technol, pp.35-1209, 2000.

J. Petzelt, S. Kamba, J. Fabry, D. Noujni, V. Porokhonskyy et al., and high frequency dielectric spectroscopy and the phase transition in Na1/2Bi1/2TiO3, p.2719, 2004.
DOI : 10.1088/0953-8984/16/15/022

Y. Amira, Y. Gagou, A. Menny, D. Mezzane, A. Zegzouti et al., Structural and Raman properties of the tetragonal tungsten bronze ferroelectric Pb2(1- x)K1+xGdxNb5O15, Solid State Comm, pp.150-419, 2010.

D. Rout, K. Moon, J. Park, and S. L. Kang, High-temperature X-ray diffraction and Raman scattering studies of??Ba-doped (Na0.5Bi0.5)TiO3 Pb-free piezoceramics, Current Applied Physics, vol.13, issue.9, 1988.
DOI : 10.1016/j.cap.2013.08.016

K. V. Lalitha, L. M. Riemer, J. Koruza, and J. , Hardening of electromechanical properties in piezoceramics using a composite approach, Appl. Phys. Lett, vol.111

D. A. Hall, A. Steuwer, B. Cherdhirunkorn, T. Mori, and P. J. Withers, A high energy synchrotron x-ray study of crystallographic texture and lattice strain in soft lead zirconate titanate ceramics, Journal of Applied Physics, vol.91, issue.8, p.4245, 2004.
DOI : 10.1103/PhysRevB.44.5

C. Bantignies, E. Filoux, R. Rouffaud, M. Pham-thi, P. Mauchamp et al.,

F. Grégoire and . Levassort, Lead-free high-frequency linear-array transducer (30 MHz) for in vivo skin imaging, IEEE International Ultrasonics Symposium, pp.785-788, 2013.