The research is devoted to the multicomponent system CaTiSiO5-YFeSnO5. The synthesis of solid solutions Ca<sub>1-x</sub>Y<sub>x</sub>Ti<sub>1-x</sub>Sn<sub>x</sub>Si<sub>1-x</sub>Fe<sub>x</sub>O<sub>5</sub> (x = 0 - 1.0, Δx = 0.1) was conducted in low-temperature plasma of hydrogen-oxygen flame. It was found that ions Ca<sup>2+</sup>, Ti<sup>4+</sup> and Si<sup>4+</sup> in the molecule of titanit may be substituted with t ions Y<sup>3+</sup>, Fe<sup>3+</sup> and Sn<sup>4+</sup>. In this case, the system produces two phases of variable composition with broad regions of homogeneity. There were defined the boundaries of formed phases, crystallographic and electrical parameters of the solid solutions. All solid solutions have a semiconductor conductivity type, whose value is linearly dependent on the temperature and com- position of the sample.
Metal oxides containing transition elements possess unique physical properties, they are subject to numerous scientific studies and are successfully used in modern electronics. Particularly complex oxides containing d- elements, including oxides having the structure of sphene (titanite CaTiSiO5) are of great practical interest.
Synthesis and study of solid solutions with the structure of sphene containing transition elements is not only of theoretical but also of practical interest. Propensity compounds with sphene form solid solutions with wide homogeneity region containing transition elements, indicates the perspective of their application as radio materials.
Possibility of full or partial replacement of the atoms in the crystal lattice of sphene leads to a natural change in the physical properties, representing both theoretical and practical interest. It was shown possibilities to replace the titanium atoms in the sphene structure with the atoms of tin [
The present communication is devoted to the study of simultaneous heterovalent substitution of all three cations in sphene: Ca2+ + Ti4+ + Si4+® Y3+ + Sn4+ + Fe3+. Simultaneous substitution of one divalent and two tetravalent (Ca, Ti, Si) atoms in a lattice of CaTiSiO5 by two trivalent and one tetravalent (Y, Fe, Sn) represents not only the theoretical but also practical interest. To solve this problem, it has been investigated previously undescribed pseudo-binary system CaTiSiO5-YFeSnO5. There was built the diagram of the system’s state and defined the crystallographic and electrical parameters of the samples of compositions (CaTiSi)1−x(YFeSn)xO5.
Synthesis of solid solutions Ca1−xYxTi1−xSnxSi1−xFexO5 (0 ≤ x ≤ 1, Δx = 0.1) was carried out in parallel in the low-temperature plasma of hydrogen-oxygen flame (LP), and ceramic technology (CT) [
Conductivity of the samples was measured by the compensation in the air, using four silver electrodes [
Comparison of x-ray diagrams of the same composition synthesized by (LP) to (CD) revealed their identity. Following is the data obtained for the samples synthesized by (NP).
Based on X-ray diagrams, it was found that in these conditions the system CaTiSiO5-YSnFeO5 form two phases (α and β) of variable composition with a wide homogeneous regions: α-phase 0 ≤ x ≤ 0.45 and β-phase 0.70 ≤ x ≤ 1.00. Samples of the composition 0.45 ≤ x ≤ 0.70 contain two phases (
α-phase. Solid solutions of compositions from CaTiSiO5 to Ca0.55Y0.45Ti0.55Sn0.45Si0.55Fe0.45O5 crystallize in the lattice sphene. Thus, replacement of up to 45% of the ions Ca2+, Ti4+ and Si4+ ions on the Y3+, Sn4+ and Fe3+ did not result in a significant rearrangement of the crystal lattice sphene (
Composition | a ± 0.01, Å | B ± 0.01, Å | C ± 0.01, Å | b ± 0.1 | dX-ray (g/cm−3) | dpycnom (g/cm−3) |
---|---|---|---|---|---|---|
CaTiSiO5 | 7.0611) | 8.7101) | 6.5681) | 113.862) | 3.524 | 3.48 |
Ca0.9Ti0.9Sn0.1Si0.9Y0.1Fe0.1O5 | 7.61 | 8.93 | 6.69 | 113.8 | 3.731 | 3.68 |
Ca0.8Ti0.8Sn0.2Si0.8Y0.2Fe0.2O5 | 8.15 | 9.14 | 6.80 | 113.8 | 3.906 | 3.89 |
Ca0.7Ti0.7Sn0.3Si0.7Y0.3Fe0.3O5 | 8.72 | 9.33 | 6.91 | 113.8 | 4.065 | 4.04 |
Ca0.6Ti0.6Sn0.4Si0.6Y0.4Fe0.4O5 | 9.28 | 9.58 | 7.03 | 113.8 | 4.196 | 4.15 |
Ca0.55Ti0.55Sn0.45Si0.55Y0.45Fe0.45 | 9.51 | 9.71 | 7.09 | 113.8 | 4.216 | 4.17 |
1)±0.005; 2)±0.02.
Input Y3+ ions occupy seven vertex polyhedral voids that were previously occupied by ions Ca2+. The radii of these ions differ little from each other: r(Y) = 0.116 nm, r(Ca) = 0.130 nm [
Despite the greater tendency of Fe3+ ions to occupy the octahedral interstices, There are numerous examples where the Fe3+ ions are in tetrahedral cavities oxygen environment such as in the crystal lattice of Fe3O4 where in the tetrahedral voids occupied 1/3 of the ions Fe3+ [
β-phase. When administered 55 at % and more ions Y3+, Fe3+ and Sn4+, instead of Ca2+, Si4+ and Ti4+ solid solutions crystallize in the orthorhombic symmetry in lattice of the psevdobrookit. The border of the homogeneity of β-phase extends in the region x = 0.70 - 1.0, which corresponds to the composition of Ca0.30Y0.70Ti0.30Sn0.70Si0.30Fe0.70O5-YFeTiO5.
The value of the lattice parameters of solid solutions of β-phase are shown in
Composition | a ± 0.01; Å | b ± 0.01; Å | c ± 0.01; Å | dX-ray (g/cm−3) | dpycnom (g/cm−3) |
---|---|---|---|---|---|
Ca0.3Ti0.3Sn0.7Si0.3Y0.7Fe0.7O5 | 9.14 | 9.52 | 3.83 | 5.962 | 5.48 |
Ca0.2Ti0.2Sn0.8Si0.2Y0.8Fe0.8O5 | 9.64 | 9.65 | 3.85 | 5.821 | 5.50 |
Ca0.1Ti0.1Sn0.9Si0.1Y0.9Fe0.9O5 | 10.13 | 9.78 | 3.87 | 5.693 | 5.49 |
YFeSnO5 | 10.7421) | 9.9251) | 3.8781) | 5.554 | 5.35 |
1)± 0.005.
As in the α-phase the increase of the value of “x” in the β-phase leads to an increase in cell volume. However, the transition from the monoclinic to the rhombohedral structure observed abrupt decrease in cell volume (
The synthesized solid solutions both α- and β-phases, are dielektriks with character of semiconductor conductivity. The determination results of conductivity, dielectric constant, the band gap, the molar polarizability and polarization of the synthesized solid solutions are shown in
As can be seen from the data presented in
The multicomponent system CaTiSiO5-YFeSnO5 was the subject of the research. It was found that ions Ca2+, Ti4+ and Si4+ in the molecule of titanit can be substituted with ions Y3+, Fe3+ and Sn4+ which leads to the formation of two phases of compositions Ca1−xYxTi1−xSnxSi1−xFexO5 with broad regions of homogeneity. There were defined the boundaries of the uniform phases at 1170 K. The samples α-phase (x = 0.0 - 0.45) crystallize in the structure of titanite. Samples b-phase (x = 0.70 - 1.0) crystallize in the orthorhombic crystal system structure
s; оm−1∙сm−1 | e | DЕ, eV | P, сm3 | |
---|---|---|---|---|
a-phase | ||||
CaTiSiO5 | 3.802 × 10−12 | 39 | 0.973 | 51.62 |
Ca0.9Ti0.9Sn0.1Si0.9Y0.1Fe0.1O5 | 5.470 × 10−12 | 39 | 0.951 | 52.37 |
Ca0.7Ti0.7Sn0.3Si0.7Y0.3Fe0.3O5 | 9.528 × 10−12 | 38 | 0.922 | 54.68 |
Ca0.6Ti0.6Sn0.4Si0.6Y0.4Fe0.4O5 | 1.439 × 10−11 | 37 | 0.900 | 56.10 |
Ca0.55Ti0.55Sn0.45Si0.55Y0.45Fe0.45 | 1.820 × 10−11 | 37 | 0.884 | 57.41 |
b-phase | ||||
Ca0.3Ti0.3Sn0.7Si0.3Y0.7Fe0.7O5 | 2.52 × 10−11 | 37 | 0.873 | 46.33 |
Ca0.2Ti0.2Sn0.8Si0.2Y0.8Fe0.8O5 | 7.907 × 10−11 | 37 | 0.833 | 49.79 |
Ca0.1Ti0.1Sn0.9Si0.1Y0.9Fe0.9O5 | 1.517 × 10−10 | 36 | 0.782 | 53.18 |
YFeSnO5 | 2.23 × 10−10 | 35 | 0.744 | 56.82 |
pseudobrookite. The electrical properties of solid solutions formed were also investigated. All samples are insulators with a semiconductor character of electrical conductivity. Complete replacement of the ions Ca2+, Ti4+ and Si4+ increases the conductivity of the samples by a factor of two.