-“Tetragonal to cubic phase transition in en Sr0.75Ba0.25HfO3“

C. HOROWITZ; R. E. ALONSO; A. LÓPEZ GARCÍA; D. LAMAS; A. CANEIRO

Madrid, España

Congreso; 10th International Meeting on ferroelectricity; 2001

CSIC

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 415 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES-AR;} p.MsoBodyText, li.MsoBodyText, div.MsoBodyText {mso-style-noshow:yes; mso-style-unhide:no; mso-style-link:"Body Text Char"; margin:0in; margin-bottom:.0001pt; text-align:justify; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES-AR;} span.BodyTextChar {mso-style-name:"Body Text Char"; mso-style-noshow:yes; mso-style-unhide:no; mso-style-locked:yes; mso-style-link:"Body Text"; mso-ansi-font-size:12.0pt; mso-ansi-language:ES-AR;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.0in 1.0in 1.0in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> Using x-ray diffraction and perturbed-angular-correlation spectroscopy, the structure and the hyperfine interactions at 181Ta probe in Sr0.75Ba0.25HfO3 respectively, have been measured. The crystalline structure was determined at room temperature and the phase transition from tetragonal to cubic lattice was observed measuring the diffractograms form 623 to 1023K in 50K steps. The two phases coexist from  673 to 973K. The spin precession curves were measured from room temperature to 1373K, in 50 K steps also. A static, asymmetric and disordered electric field gradient model was used to fit these time spectra. At room temperature the hyperfine parameters wQT = 23.92 Mrad/s, hT = 0.462 and dT = 23.55 % were obtained. As the temperature increases the hyperfine parameters changed: wQ diminishes, h is almost constant and d diminishes to almost zero. This interaction was observed to be unique up to 673 K. Above this temperature a second site appeared and this two phases coexist up to 923K. From this temperature the second phase was only observed. During the phase transformation the population of the tetragonal phase fT, hT and dT tend to zero and wQT = 13.76 Mrad/s. The hyperfine parameters corresponding to the cubic phase have a different temperature behavior: wQC decreases with different slopes, hC is almost constant and dC increases from zero to » 16 %. From fT(T) an activation energy of 0.6218 eV was determined.