UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-23 13:39
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Conference: Bucharest University Faculty of Physics 2008 Meeting


Section: Solid State Physics and Materials Science


Title:
Polimorfic diagram of the Ba1-xSrxTiO3 ceramics


Authors:
V. GHITA, Roxana RADU, I. SMARANDA, Luminita CRISTESCU, H.V. ALEXANDRU, C. BERBECARU


Affiliation:
University of Bucharest, Faculty of Physics, Bucharest-Magurele, Romania


E-mail
lumicrist21@yahoo.com, roxana.radu@yahoo.com, valentin.ghita@yahoo.com, smaranda_nusi@yahoo.com, berbecaru2ciceron.yahoo.com,horia@infim.ro


Keywords:
BST ceramics, SEM, XRD investigations, permittivity measurements


Abstract:
Due to their high technological importance, especially in the microwave domain Ba1-xSrxTiO3 (BST) ceramics are intensively studied. The BST ceramics with Sr content x = 0.25, 0.35, 0.40, 0.50, 0.60, 0.75 and 0.90 were prepared by standard solid-state reaction and sintered at 1210÷1260 oC/2h [1,2]. To investigate pores in the structure, the grains morphology and their dimensions, polished and etched samples were used in SEM analysis. X-ray diffraction show a pervoskite structure of BST ceramics at room temperature. For x ≤ 0.35 BST samples exhibit a tetragonal unit cells at room temperature. For increased Sr content, x ≥ 0.40 BST samples have cubic structures. The dependence of the permittivity and loss were measured on the temperature range –150  +150 deg C with a HIOKY3511-50, RLC automatic bridge at 1 kHz. The transitions (cubic – tetragonal – orthorhombic - rhombic) of the ceramics strongly depend on the Sr content. We have found a linear dependence for all three transitions increasing the Sr content. The transition (4mm)–(mm2) and (mm2)–(3m) lines meet each other at x = 0.78 concentration values. The (m3m)–(4mm) and (4mm–3m) lines transition meet each other at x = 0.84 value. Both points agree with the Gibbs rule of the phase transition at constant pressure, [3]. References: [1] H.V. Alexandru, C. Berbecaru, A. Ioachim et al., Mat. Sci. and Eng. B, 109 152 (2004). [2] A. Ioachim, M.I. Toacsan, M.G. Banciu et al., Thin Solid Films, 515 6289 (2007). [3] Berbecaru C., Alexandru H.V. et al, Thin Solid Films,(2008), - to be published.