通过流延成型技术,以片状K0.5Na0.5NbO3(简称为KNN)粉体为模板,结合掺杂改性后的基料粉体(K0.45Na0.55)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3-0.005Ba ZrO3(简称为KNNLST-BZ)流延制备出KNN基无铅压电陶瓷,研究了不同的工艺参数(烧结温度、...通过流延成型技术,以片状K0.5Na0.5NbO3(简称为KNN)粉体为模板,结合掺杂改性后的基料粉体(K0.45Na0.55)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3-0.005Ba ZrO3(简称为KNNLST-BZ)流延制备出KNN基无铅压电陶瓷,研究了不同的工艺参数(烧结温度、烧结次数)对于KNNLST-BZ织构化陶瓷的电学性能、显微结构的影响。结果表明:模板含量为20wt%的KNNLST-BZ织构化陶瓷在1145℃下保温2 h呈现出优异的性能:压电常数d33=204 p C/N,横向机电耦合系数k31=23%,剩余极化强度Pr=26μC/cm2,矫顽场Ec=1.2 k V/mm。同时该织构化陶瓷在1145℃下烧结2次能得到更优的电学性能:d33=248 p C/N,k31=32.54%,Pr=38μC/cm2,Ec=1.2 k V/mm,介电损耗tanδ=6.38%,机械品质因数Qm=16.76,介电常数εT33/ε0=913.7,横向伸缩振动频率常数N1=2244。展开更多
The electronic structures, Born effective charges（BECs）, and full phonon dispersions of cubic, tetragonal, orthorhombic, and rhombohedral K0.5Na0.5Nb O3 are investigated by the first principles method based on densi...The electronic structures, Born effective charges（BECs）, and full phonon dispersions of cubic, tetragonal, orthorhombic, and rhombohedral K0.5Na0.5Nb O3 are investigated by the first principles method based on density functional theory.The hybridized states of Nb 4d and O 2p states are observed in the valence band, showing the formation of a strong Nb–O covalent bond which should be responsible for the displacement of Nb and O atoms. The abnormally large BECs of Nb and O indicate the possibility of phase instability induced by the off-center displacement of Nb and O atoms. The phonon dispersions reveal that the ferroelectric instability of K0.5Na0.5Nb O3 is dominated by Nb and O displacements with significant Na characteristics. In addition to the ferroelectric instability, there is also rotational instability coming from the oxygen octahedra rotation around one axis. Moreover, the Γ phonon properties of orthorhombic KNb O3, Na Nb O3, and K0.5Na0.5Nb O3 are also studied in detail.展开更多
Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with K0.5Na0.5NbO3 (KNN) nanocrystallites of different volume fraction using the hot-pressing technique.For comparison,PVDF-KN...Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with K0.5Na0.5NbO3 (KNN) nanocrystallites of different volume fraction using the hot-pressing technique.For comparison,PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the studies of the crystallite size (wide range) effect on the dielectric and piezoelectric properties.The structural,morphological,dielectric,and piezoelectric properties of these nano and micro crystal composites were investigated.The incorporation of KNN fillers in PVDF at both nanometer and micron scales above 10 vol％ resulted in the formation of polar β-form of PVDF.The room temperature dielectric constant as high as 3273 at 100 Hz was obtained for the PVDF comprising 40 vol％ KNN nanocrystallites due to dipole-dipole interactions (as the presence of β-PVDF is prominent),whereas it was only 236 for the PVDF containing the same amount (40 vol％) of micron-sized crystallites of KNN at the same frequency.Various theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and micro crystal composites.The PVDF comprising 70 vol％ micron-sized crystallites of KNN exhibited a d33 value of 35 pC/N,while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to the unrelieved internal stress within each grain,besides the fact that they have less domain walls.展开更多
文摘通过流延成型技术,以片状K0.5Na0.5NbO3(简称为KNN)粉体为模板,结合掺杂改性后的基料粉体(K0.45Na0.55)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3-0.005Ba ZrO3(简称为KNNLST-BZ)流延制备出KNN基无铅压电陶瓷,研究了不同的工艺参数(烧结温度、烧结次数)对于KNNLST-BZ织构化陶瓷的电学性能、显微结构的影响。结果表明:模板含量为20wt%的KNNLST-BZ织构化陶瓷在1145℃下保温2 h呈现出优异的性能:压电常数d33=204 p C/N,横向机电耦合系数k31=23%,剩余极化强度Pr=26μC/cm2,矫顽场Ec=1.2 k V/mm。同时该织构化陶瓷在1145℃下烧结2次能得到更优的电学性能:d33=248 p C/N,k31=32.54%,Pr=38μC/cm2,Ec=1.2 k V/mm,介电损耗tanδ=6.38%,机械品质因数Qm=16.76,介电常数εT33/ε0=913.7,横向伸缩振动频率常数N1=2244。
基金Project supported by the Jiangxi Provincial Natural Science Foundation,China(Grant No.20122BAB216007)the Foundation of Jiangxi Provincial Educational Committee,China(Grant No.GJJ14648)
文摘The electronic structures, Born effective charges（BECs）, and full phonon dispersions of cubic, tetragonal, orthorhombic, and rhombohedral K0.5Na0.5Nb O3 are investigated by the first principles method based on density functional theory.The hybridized states of Nb 4d and O 2p states are observed in the valence band, showing the formation of a strong Nb–O covalent bond which should be responsible for the displacement of Nb and O atoms. The abnormally large BECs of Nb and O indicate the possibility of phase instability induced by the off-center displacement of Nb and O atoms. The phonon dispersions reveal that the ferroelectric instability of K0.5Na0.5Nb O3 is dominated by Nb and O displacements with significant Na characteristics. In addition to the ferroelectric instability, there is also rotational instability coming from the oxygen octahedra rotation around one axis. Moreover, the Γ phonon properties of orthorhombic KNb O3, Na Nb O3, and K0.5Na0.5Nb O3 are also studied in detail.
文摘Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with K0.5Na0.5NbO3 (KNN) nanocrystallites of different volume fraction using the hot-pressing technique.For comparison,PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the studies of the crystallite size (wide range) effect on the dielectric and piezoelectric properties.The structural,morphological,dielectric,and piezoelectric properties of these nano and micro crystal composites were investigated.The incorporation of KNN fillers in PVDF at both nanometer and micron scales above 10 vol％ resulted in the formation of polar β-form of PVDF.The room temperature dielectric constant as high as 3273 at 100 Hz was obtained for the PVDF comprising 40 vol％ KNN nanocrystallites due to dipole-dipole interactions (as the presence of β-PVDF is prominent),whereas it was only 236 for the PVDF containing the same amount (40 vol％) of micron-sized crystallites of KNN at the same frequency.Various theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and micro crystal composites.The PVDF comprising 70 vol％ micron-sized crystallites of KNN exhibited a d33 value of 35 pC/N,while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to the unrelieved internal stress within each grain,besides the fact that they have less domain walls.
