Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

Abstract

2016-11-02T18:49:00

Piezoelectric, Mechanical and Acoustic Properties of KNaNbOF5 from First-Principles Calculations

“…Compared with ZnO, the piezoelectric constants of α-KNaNbOF 5 are much lower. In order to make a comparison to the experimental piezoelectric response measurement reported in [ 9 ], the calculated piezoelectric stress matrix [ e ] is converted into the piezoelectric strain matrix [ d ] by the relationship [ e ] = [ c ][ d ], where [ c ] is the elastic matrix. Based on Table 4 and Table 5 , the calculated d z3 is 1.5 pC/N, which is lower than the experimental value 6.7 pC/N [ 9 ].…”

“…In order to make a comparison to the experimental piezoelectric response measurement reported in [ 9 ], the calculated piezoelectric stress matrix [ e ] is converted into the piezoelectric strain matrix [ d ] by the relationship [ e ] = [ c ][ d ], where [ c ] is the elastic matrix. Based on Table 4 and Table 5 , the calculated d z3 is 1.5 pC/N, which is lower than the experimental value 6.7 pC/N [ 9 ]. Since our calculated lattice parameters, atomic positions, and relative permittivity agree well with experiments, the errors in the calculated d z3 may originate from three aspects: (1) The experiment was carried out at room temperature—since finite temperatures are not included in the calculation, the calculated value of d z3 is smaller than that observed in experiments; (2) The value of d z3 is sensitive to the crystal structure—the calculated lattice constants deviate from the experimental values by ~1%, which affects the evaluation of d z3 ; (3) Compared to other commonly used piezoelectric materials, such as BaTiO 3 (~190 pC/N) and K 0.5 Na 0.5 NbO 3 (~160 pC/N) [ 9 ], the d z3 value of KNaNbOF 5 is much lower.…”

“…Secondly, KNaNbOF 5 is also a triboluminescent material. It was reported that strong triboluminescence can be visible to the naked eye under normal lighting conditions [ 9 ]. Last but not least, KNaNbOF 5 has attracted great interest due to its polymorphism [ 10 , 11 ].…”

High Ionic Conductivity in Oxygen-Deficient Ti-Substituted Sodium Niobates and the Key Role of Structural Features

“…17 Taking into account the ionic radii ratio with cations in A and B sites, for r(A n+ )/r(B m+ ) > 1.80, the 3D or 2D perovskite network is generally stabilized whereas the pyrochlore structure is obtained for 1.46 < r(A n+ )/r(B m+ ) < 1.80 and finally the fluorite framework is favored for r(A n+ )/r(B m+ ) < 1. 46. The introduction of vacancies at the A site promotes cation ordering and the formation of superstructures evidenced, for instance, in tetragonal or hexagonal tungsten bronzes.…”

“…42,43 Polar phases can be stabilized as sodium cations are partly substituted for lithium (Li x Na 1-x NbO 3 ) 44 and also when fluorine substitutes partially oxygen (KNaNbOF 5 ). 45,46 No Ti-substituted sodium niobate with a polar structure has ever been reported so far. In the present work, the synthesis of NaNb 1-x Ti x O 3-0.5x , 0 < x ≤ 0.20 is reported, starting with hydrothermal conditions.…”