KNbO3 Solid Solutions Research Articles

Local structure analysis of BaTiO3–KNbO3 solid solution

The atomic-scale structure of a solid solution of BaTiO3 (BT) and KNbO3 (KN) has been studied using high-energy X-ray diffraction, X-ray absorption fine structure, and atomic pair-distribution function analysis techniques. We prepared BT–KN solid solution using KNbTiO5, in which Ti and Nb atoms are arranged randomly. The average structure of the BT–KN solid solution was cubic and the local structure is also reproduced by the cubic structure. It is rare that a solid solution synthesized from ferroelectric materials has the local structure of a paraelectric material. Since the original correlation of BT or KN was lost, ferroelectricity disappeared in the BT–KN solid solution.

Growth of KTN crystals by double crucible Czochralski method

Potassium tantalite niobate (KTa1−xNbxO3, KTN) single crystals with various compositions and sizes were grown by double crucible Czochralski method in KTaO3–KNbO3 solid solution system. All the crystals we have grown are in good transparence and are >1 cm in size. Growth habit, morphological, structural and homogeneity properties of five different compositions of KTN crystals, including KTaO3, KTa0·91Nb0·09O3, KTa0·81Nb0·19O3, KTa0·75Nb0·25O3 and KTa0·63Nb0·37O3, are investigated in this work. Electron probe microanalysis shows that the composition fluctuation of KTN crystal is <0·0003 cm−1. X-ray diffraction experimental results show that all crystals belong to cubic phase at room temperature. Lattice parameters a are 3·984∼3·994 Å, which corresponded to the composition of x = 0∼0·37. High resolution XRD measurement shows that all KTN crystals are in high integrity and good quality. Our work shows that the KTN crystals we have grown are in good quality and have a broad application prospects.

Growth and Properties of Cubic Potassium Tantalate Niobate Crystals

Cubic KTa1-xNbxO3single crystals with difference compositions have been grown by Czochralski technique in KTaO3- KNbO3solid solution system. Growth habit, morphological feature, and other properties of two different composition KTN crystals, KTa0.65Nb0.35O3, and KTa0.63Nb0.37O3are investigated in this work. The X-ray diffraction (XRD) experimental results show that all crystals belong to cubic phase at room temperature, lattice parameterais 3.993 and 3.994Å corresponded to the composition of x (Nb) =0.35, 0.37, respectively. HXRD and AFM measurement results show all KTN crystals are in high integrity and good quality. The transmittance spectra of KTN crystals show that the cut off wavelength of KTN crystals decreased with the Nb increasing in the crystal. The dielectric-temperature measurement results shows KTN crystal have optimal performance on Kerr effect at the Currie temperature of the crystal. All the results show that the KTN crystals we grown are in good quality and have a broad application prospects

ChemInform Abstract: Preparation of KTaO3 and KNbO3 Solid Solutions Through Sol-Gel Processing.

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Ferroelectric behaviour and phase diagrams of SrTiO3-based solid solutions

Ceramic samples of Sr1-xCdxTiO3 and (1-x)SrTiO3–(x)KNbO3 solid solutions were investigated using a dielectric technique in the temperature range from 4.2 K to 300 K at frequencies of 1 kHz and 1 MHz. Phase diagrams of these systems are derived. It is shown that there are ferroelectric phase transitions in Sr1-x Cd x TiO3 for x values 0.01 ≤ x 0.05 and 0.85 ≤ x ≤ 1. In pure CdTiO3 the temperature dependence of the spontaneous polarization was obtained from ferroelectric hysteresis loops. At x value between x = 0.005 and x = 0.01, Sr1-x Cd x TiO3 undergoes a low-temperature transformation from the ferroelectric to a polar glasslike state. At low x, the transition temperature Tc varies as (x—x c)1/2 With x c ≈ 0.002 for Sr1-x Cd x TiO3 and x c ≈ 0.007 for (1-x)SrTiO3-(x)KNbO3. A polar state in (1-x)SrTiO3-(x)KNbO3 at x c ≤ x ≤ 0.2 has some features of a glasslike behavior.

Preparation of KTaO3 and KNbO3 Solid Solutions through Sol–Gel Processing

Potassium tantalate–niobate solid‐solution (KTN) powders and thin films were prepared from metallo–organic compounds through sol–gel processing. The KTN precursors were chemically modified and then prehydrolyzed with various concentrations of water. The stability of the modified solutions and the effects of prehydrolysis on the crystallization are discussed. Powder gels were obtained by exposing the solution to the atmospheric water, hydrolyzing the solutions. Alternatively, thin films were deposited on fused silica, silicon, sapphire, MgO, and SrTiO3, using the spinning technique. The pyrolysis and crystallization of KTN powders and films were investigated by differential thermal analysis, theromogravimetric analysis, and X‐ray diffraction. The effects of substrate and other processing parameteres on the crystal structure of the KTN phases were also investigated. KTN powders crystallized into a perovskite phase regardless of the processing conditions. The crystal structure of the KTN thin films had a strong dependency on the crystal structure of the substrates, while other processing parameters played smaller roles. Pyrochlore KTN was the major phase that crystallized on fused silica and silicon, whereas oriented perovskite KTN was obtained on single‐crystal MgO and SrTiO3.

Electrical, X‐Ray, and Thermal Expansion Studies in the System KNbO3‐AgNbO3

Unlike the KNbO3‐NaNbO3 system, the KNbO3‐AgNbO3 system possessed a very limited degree of solid solution between its end‐members. Solid solution of AgNbO3 in KNbO3 was limited to slightly less than 6 mole %, and solid solution of KNbO3 in AgNbO3 was limited to less than 0.5 mole %. Because of a tendency for the K1‐xAgxNbO3 system to lose oxygen spontaneously during firing when 0.06 ≤x≤ 0.995, the system could not be treated as a true binary system. The compositions in the KNbO3 solid solution region (0 ≤x &lt; 0.06) were ferroelectric at room temperature. Lattice parameter, relative permittivity, and thermal expansion measurements were made on specimens in the region 0 ≤x≤ 0.06.

Phase Transitions in the System BaTiO3-KnbO3

Solid solution formation in the system BaTiO3—KnbO3 was established by X-ray diffraction and dielectric measurements. Solid solutions with cubic symmetry were observed in the composition range from 4 to 90 mole % KnbO3 at room temperature. The lattice parameter for the BaTiO3 solid solutions increased with increasing KNbO3; that for the KnbO3 solid solutions decreased with the addition of BaTiO3. A distinct discontinuity in lattice parameter was observed at the composition containing about 65 mole % BaTiO3. Dielectric measurements were made from-195° to 400°C. The cubic-tetragonal transition temperature of BaTiO3 was rapidly lowered with increasing addition of KNbO3, whereas the two lower phase transition temperatures were raised. All three phase transitions of KnbO3 were rapidly lowered with increasing addition of BaTiO3. The observed phase transitions, lattice parameters, and electron probe data suggest a complex region in the subsolidus which extends from 35 to about 75 mole % KNbO3.