| Transparent ferroelectric ceramics is a kind of significant new functional materials which are competited fiercly in the international materials field. Because they not only have excellent ferroelectric, piezoelectric, pyroelectric electronic, mechanical properties, but also have outstanding electro-optic effect, thermostability, corrosion resistance, high rigidity and high transparent characteristics, the ceramics will be used as the key materials of light computer, electronic information technology and national defense military application in the future. In this article, the potassium sodium niobate based transparent ferroelectric ceramics have been prepared successfully by sealed pressureless sintering. The effects of preparation technology on the transmittance and ferroelectric properties for the ceramics have been studied. And the relationships of crystal structure, density, transmittance, dielectric, ferroelectric and piezoelectric properties have been investigated to discuss the physical mechanism of transparency. The main conclusions as follow:(1) The KNN-CSN9-Sealed sample prepared by sealed pressureless sintering has higher RD of 98% when that of KNN-CSN9-Unsealed is 95%. The EDS of fracture surface for the samples demonstrates that the loss of K+, Na+i ons in KNN-CSN9-Sealed was less than that of KNN-CSN9-Unsealed sample, and the KNN-CSN9-Sealed sample had higher density. The transmission of KNN-CSN9-Sealed sample at 1064nm is 60%, which is 15% higher than that of KNN-CSN9-Unsealed sample (45%). The electrical properties of KNN-CSN9-Sealed sample are superior to that of the KNN-CSN-Unsealed sample through the comparison between the two samples. The best sintering temperature of KNN-CSN9 is 1220℃ for 4h.(2) The crystal structure of(1-x) KNN-xCSN samples is pure perovskite structure. With increasing of CSN content, the phase structure of samples transformed from orthogonal to tetragonal and then to pseudo cubic. The maximum RD and transmittance at 1064 nm are 98% and 60% whenx=0.090, respectively. The temperature dependences of dielectric constant also shows a phase structure transformation from orthogonal to tetragonal and then to pseudo cubic. With increasing of CSN content, the maximum dielectric constant of samples increased first and then decreased, and the maximum is 3279 at x=0.090, the Tc of the sample is 147℃. The (1-x) KNN-xCSN samples are relaxor ferroelectrics. The Curie constant C shows that the cause of high temperature paraelectric phase in the samples is displacement of transition. Otherwise, with increasing of CSN, the △Tm and diffusion factor γ of samples increased first and then decreased, and the maximum △Tm= 161℃ and γ=1.85 obtained at x=0.090. The KNN-CSN9 sample also has good properties of ferroelectric and piezoelectric, the remnant polarization Pτ= 6.88 μC/cm2, the coercive field Ec=8.49 kV/cm and the piezoelectric constant d33=35 pC/N.(3) The crystal structure of 0.91KxNa1-xN-0.09CSN samples is pure perovskite structure; and the structures of samples are all pseudo cubic with no MPB. The maximum RD and transmittance at 1064 nm are 99% and 61% when x=0.41, respectively. With increasing of K+ content, the Tc decreased first and then increased, the minimum Tc-118 ℃ obtained at x=0.50, and εm of the sample is 2559. With increasing of the K+ content, the △rm and the diffusion factor γ of samples all increased first and then decreased,the maximum △Tm= 178℃ and γ= 1.79 obtained at x=0.50. The Pr and of samples reduced when x≦0.455, and the Pr stayed when x>0.45. The samples show a region around x= 0.50 with superior electrical properties.(4) The crystal structure of (1-x) KNN-xSSN is pure perovskite structure. With increasing of SSN content, the phase structure of samples transformed from orthogonal to pseudo cubic. The maximum RD and transmittance at 1064 nm are 99% and 63% at x =0.07, respectively. With increasing of SSN content, the temperature dependences of dielectric constant on samples also shows the structure transformation from orthogonal to pseudo cubic; the introduction of SSN had decreased the Tc and broadened the Curie peak. With increasing of SSN, the △Tm and y of samples increased first and then decreased, the maximum ATm obtained at x=0.07 but the maximum γ=1.73 obtained at x=0.07. With increasing of SSN content, the Pr and Ec decreased first and then increased, the minimum Pr and Ec were obtained at x=0.07. At the time time, the d33 reduced with increasing of SSN content, and the d33 of the samples reduced intensively when x≦0.70 and decreased slowly when x> 0.70.(5) The 0.91KNN-0.09CSN and 0.93KNN-0.07SSN samples exhibits a perovskite structure with pseudo cubic. Their RD are 98%,99%, respectively. And their transmittance at 1064 nm are 60%,63%. The 0.91KNN-0.09CSN sample showed superior electrical properties to the 0.93KNN-0.07SSN sample. |
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