PIEZOELECTRIC PROPERTIES OF Bi_2TeO_5 SINGLE CRYSTALS

Abstract

This paper is devoted to the measurement results of piezoelectric, dielectric and elastic tensor components in the temperature range between 20• C and 400• C. It was revealed that excitation resonance and antiresonance signals were possible without preliminary sample polarizing. Besides, the sound velocities measured along the main axes by echo-pulse method at room temperature are presented. Key words: piezoelectric, dielectric, elastic constants, sound velocity PACS: 77.84Bismuth tellurite (BTO) single crystals are of piezoelectric material but their electromechanical properties have not been practically studied. In [1] there are some data concerning these properties in BTO. The coupling factor k 15 = 0.274 at room temperature presented in the work [2] is prospective enough to be used as the main elements of electromechanical transducers. This fact suggested us to continue studying these properties of Bi 2 TeO 5 . This paper presents the results of investigating the piezoelectric, dielectric and elastic properties of bismuth tellurite single crystals between 20• C and 400• C (besides the sound velocity vector components which were measured at room temperature). Bi 2 TeO 5 is a polar single crystal belonging to the Abm2 space group. It possesses the orthorhombic symmetry and the fluorite-type structure with the unit-cell parameters a = 11.602Å, b = 16.461Å, c = 5.523Å [5].Single crystals of BTO were grown using the Czochralski method. The melt was prepared from ultra high purity Bi 2 O 3 and TeO 2 at the ratio 47 and 53 mole % respectively just like in the work [4]. The crystal boules were cut along the main crystallographic axes in the form of plates and bars for corresponding coefficients. The cuts in the form of bars were executed in "a"-plane at the angles of 30• and 45• to "b"-axis. The sizes of the plates and bars were selected so as to excite the necessary vibrations. The plates were used to obtain d 15 and d 24 piezoelectric coc A

Phase Formation and Crystal‐Structure Determination in the Bi2O3–TiO2–TeO2 System Prepared in an Oxygen Atmosphere

“…3, the crystal structure of Bi 2 Ti 3 TeO 12 is based on a hexagonal closest packing of oxygen, with one half of the octahedral interstices occupied by cations. Ti and Te are statistically interchangeable and occupy, in an ordered fashion, two thirds of the octahedral interstices in every second layer, thus forming (Ti 0.75 Te 0.25 )O 3 sheets that are isostructural with boehmite (Al(OH) 3 ). Bi occupies one-third of the octahedral interstices in the layer between, so that it has the empty interstices above and below (avoiding short contact with the (Ti 0.75 Te 0.25 ) sites).…”

“…The interatomic distances and the angular ranges are given in Table VI. As one can see, the octahedra (Ti,Te)O 6 are rather distorted and the octahedra BiO 6 (2) 0.059 (6) 0.755 (7) 0.002(5) O(2) 0.841 (3) 0.602 (6) 0.593 (7) 0.002(5) O(3) 0.061 (3) 0.552 (6) 0.884 (7) 0.002(5) O(4) 0.809 (3) 0.906 (6) 0.970 (7) 0.002 (5) even more so. At an intermediate stage of the refinement, restraints were applied for the ''problematic'' angles.…”

“…O wing to their specific physical properties, which make them attractive for various industrial applications, attention has already been focused on several compounds from the subordinated binaries of the Bi 2 O 3 –TiO 2 –TeO 2 system. The ceramics from this system can be applied as non‐volatile memory elements, as dielectrics in low‐temperature cofired ceramic (LTCC) technology, as piezoelements, as oxygen ion conductors, etc 1–6 . In addition to the applications of crystalline compounds, Ti‐containing tellurite glasses were also shown to be promising electro‐optical materials 7,8 …”

“…The ceramics from this system can be applied as non-volatile memory elements, as dielectrics in low-temperature cofired ceramic (LTCC) technology, as piezoelements, as oxygen ion conductors, etc. [1][2][3][4][5][6] In addition to the applications of crystalline compounds, Ticontaining tellurite glasses were also shown to be promising electro-optical materials. 7,8 The most exhaustive studies were performed on the binary Bi 2 O 3 -TiO 2 system.…”