Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5O15 and lead pyrochlore ( Pb2Nb2O7 )
| Autor: | Siân E. Dutton, S. E. Rowley, Jack Hodkinson, Catarina Ferraz, Finlay D. Morrison, James F. Scott, Jonathan Gardner, Rebecca M. Smith, Michael A. Carpenter, Jiasheng Chen |
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| Rok vydání: | 2018 |
| Předmět: |
Phase transition
Materials science Physics and Astronomy (miscellaneous) Transition temperature Pyrochlore 02 engineering and technology engineering.material 021001 nanoscience & nanotechnology 01 natural sciences Heat capacity Tetragonal crystal system Crystallography Quantum critical point 0103 physical sciences engineering General Materials Science Orthorhombic crystal system 010306 general physics 0210 nano-technology Absolute zero |
| Zdroj: | Physical Review Materials. 2 |
| ISSN: | 2475-9953 |
| DOI: | 10.1103/physrevmaterials.2.084409 |
| Popis: | We have synthesized ceramic specimens of the tetragonal tungsten bronze ${\mathrm{K}}_{3}\mathrm{L}{\mathrm{i}}_{2}\mathrm{T}{\mathrm{a}}_{5}{\mathrm{O}}_{15}$ (KLT) and characterized its phase transition via x-ray diffraction, dielectric permittivity, resonant ultrasonic spectroscopy, and heat capacity measurements. The space group of KLT is reported as both $P4/mbm$ and $Cmmm$ with the orthorhombic distortion occurring when there are higher partial pressures of volatile K and Li used inside the closed crucibles for the solid state synthesis. The data show strong relaxor behavior, with the temperature at which the two dielectric relative permittivity peaks decreasing, with $104\ensuremath{\ge}{T}_{m1}\ensuremath{\ge}69\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and $69\ensuremath{\ge}{T}_{m2}\ensuremath{\ge}46\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ as probe frequency $f$ is reduced from 1 MHz to 316 Hz. $F$ tests show that the data satisfies a Vogel-Fulcher model better than Arrhenius with an extrapolated freezing temperature for ${\ensuremath{\varepsilon}}^{\ensuremath{'}}$ and ${\ensuremath{\varepsilon}}^{\ensuremath{''}}$ of ${T}_{f1}=+15.8$ and $\ensuremath{-}11.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{f2}=\ensuremath{-}5.0$ and $\ensuremath{-}15.0\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\phantom{\rule{4pt}{0ex}}f\ensuremath{\rightarrow}0$ (tending to dc). This difference between ${T}_{f}$ from real and imaginary values, albeit counterintuitive, is mandatory, according to the theory of Tagantsev. Therefore, by tuning frequency, the transition could be shifted to absolute zero, suggesting KLT has a relaxor-type quantum critical point. In addition, we have reanalyzed the conflicting literature for $\mathrm{P}{\mathrm{b}}_{2}\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{7}$ pyrochlore which suggests that this also has a relaxor-type quantum critical point since the freezing temperature from the Vogel-Fulcher fitting is below absolute zero. Since the transition temperature evidenced in the dielectric data at approximately 100 kHz shifts below 0 K for very low frequencies, this transition would not be seen with heat capacity data collected in the zero-frequency (dc) limit. Both of these materials show promise for possible new relaxor-type quantum critical points with nonperovskite based structures. |
| Databáze: | OpenAIRE |
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