The effect of internal pressure on the tetragonal to monoclinic structural phase transition in ReOFeAs: the case of NdOFeAs. Fratini, M., Caivano, R., Puri, A., Ricci, A., Ren, Z., Dong, X., Yang, J., Lu, W., Zhao, Z. X., Barba, L., Arrighetti, G., Polentarutti, M., & Bianconi, A. Superconductor Science and Technology, 21(9):092002+, 2008.
The effect of internal pressure on the tetragonal to monoclinic structural phase transition in ReOFeAs: the case of NdOFeAs [link]Paper  doi  abstract   bibtex   
We report the temperature dependent x-ray powder diffraction of the quaternary compound NdOFeAs (also called NdFeAsO) in the range between 300 and 95 K. We have detected the structural phase transition from the tetragonal phase, with P 4/ nmm space group, to the orthorhombic or monoclinic phase, with Cmma or P 112/ n (or P 2/ c ) space group, over a broad temperature range from 150 to 120 K, centered at T 0 ∼137 K. Therefore the temperature of this structural phase transition is strongly reduced, by about ∼30 K, by increasing the internal chemical pressure going from LaOFeAs to NdOFeAs. In contrast, the superconducting critical temperature increases from 27 to 51 K going from LaOFeAs to NdOFeAs doped samples. This result shows that the normal striped orthorhombic Cmma phase competes with the superconducting tetragonal phase. Therefore by controlling the internal chemical pressure in new materials it should be possible to push toward zero the critical temperature T 0 of the structural phase transition, giving the striped phase, in order to get superconductors with higher T c .
@article{fratini_effect_2008,
	title = {The effect of internal pressure on the tetragonal to monoclinic structural phase transition in {ReOFeAs}: the case of {NdOFeAs}},
	volume = {21},
	issn = {0953-2048},
	url = {http://dx.doi.org/10.1088/0953-2048/21/9/092002},
	doi = {10.1088/0953-2048/21/9/092002},
	abstract = {We report the temperature dependent x-ray powder diffraction of the quaternary compound NdOFeAs (also called NdFeAsO) in the range between 300 and 95 K. We have detected the structural phase transition from the tetragonal phase, with P 4/ nmm space group, to the orthorhombic or monoclinic phase, with Cmma or P 112/ n (or P 2/ c ) space group, over a broad temperature range from 150 to 120 K, centered at T 0 ∼137 K. Therefore the temperature of this structural phase transition is strongly reduced, by about ∼30 K, by increasing the internal chemical pressure going from LaOFeAs to NdOFeAs. In contrast, the superconducting critical temperature increases from 27 to 51 K going from LaOFeAs to NdOFeAs doped samples. This result shows that the normal striped orthorhombic Cmma phase competes with the superconducting tetragonal phase. Therefore by controlling the internal chemical pressure in new materials it should be possible to push toward zero the critical temperature T 0 of the structural phase transition, giving the striped phase, in order to get superconductors with higher T c .},
	number = {9},
	journal = {Superconductor Science and Technology},
	author = {Fratini, Michela and Caivano, Rocchina and Puri, Alessandro and Ricci, Alessandro and Ren, Zhi-An and Dong, Xiao-Li and Yang, Jie and Lu, Wei and Zhao, Zhong X. and Barba, Luisa and Arrighetti, Gianmichele and Polentarutti, Maurizio and Bianconi, Antonio},
	year = {2008},
	keywords = {feas, iron, lao, ndo, phase-diagram, phase-transition, strain, structural, super, temperature, xrd},
	pages = {092002+}
}
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