# Comparative Review on Thin Film Growth of Iron-Based Superconductors

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## Abstract

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## 1. Introduction

## 2. Historical Overview of Film Fabrication of Iron-Based Superconductors

#### 2.1. 1111-System

#### 2.2. 122-System

#### 2.3. 11-System

#### 2.4. 11-System ML

## 3. Substrate Materials in the Films Fabrication of Iron-Based Superconductors

## 4. Comparison in Phase Diagram between Bulk Single Crystal and Epitaxial Thin Films in 11 System

## 5. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 2.**Dependence of lattice parameters and ${T}_{\mathrm{c}}$ for NdFeAs(O,F) films [189], SmFeAs(O,F) films [190], Ba(Fe${}_{1-x}$Co${}_{x}$)${}_{2}$As${}_{2}$ films [51,63], and FeSe${}_{0.5}$Te${}_{0.5}$ films [40,52,191] on the coefficient of thermal expansion at 300 K, ${\alpha}_{300\mathrm{K}}$.

**Figure 3.**Phase diagrams in (

**a**) bulk samples [27,198,199,200,201,202] and (

**b**) films of FeSe${}_{1-x}$Te${}_{x}$. Blue circles (red circles) and orange hexagons (light-green stars) represent ${T}_{\mathrm{c}}^{\mathrm{onset}}$ and ${T}_{s}$ of the FeSe${}_{1-x}$Te${}_{x}$ thin films fabricated on LAO [133] (CaF${}_{2}$ [131,132,209]) , respectively. In the inset, the dependence of ${T}_{\mathrm{c}}^{\mathrm{onset}}$ on Te content x is shown. The values of ${T}_{\mathrm{c}}$ for bulk samples estimated from the magnetic susceptibility measurements are shown as gray triangles [27,198]. The dashed curves in the inset are guides for the eye. The words of “ortho.”, “tetra.”, “mono.”, and “AF” are abbreviations for orthorhombic, tetragonal, monoclinic phases, and bicollinear antiferromagnetic-ordered state, respectively.

**Figure 4.**Temperature dependence of resistivity, $\rho $, for FeSe${}_{1-x}$Te${}_{x}$ films on (

**a**) CaF${}_{2}$ and (

**b**) LaAlO${}_{3}$ substrates.

**Figure 5.**Temperature dependence of (

**a**) resistivity, $\rho $; and (

**b**) $dlog\rho /dT$ for FeSe film on LaAlO${}_{3}$ and FeSe${}_{1-x}$Te${}_{x}$ films on CaF${}_{2}$ with $x=0,0.1,0.3$; Kohler Plot of (

**c**) FeSe film on LaAlO${}_{3}$ and FeSe${}_{1-x}$Te${}_{x}$ films on CaF${}_{2}$ with (

**d**) $x=0$; (

**e**) $x=0.1$; and (

**f**) $x=0.3$.

**Figure 6.**(

**a**) Schematic crystal structure of FeSe${}_{1-x}$Te${}_{x}$; (

**b**) Front view of FeSe${}_{1-x}$Te${}_{x}$.

**Figure 7.**Te content dependence of (

**a**) bond angle, $\alpha $; and (

**b**) Chalcogen height, h, for FeSe${}_{1-x}$Te${}_{x}$ films on CaF${}_{2}$ and LAO substrates. The data for FeSe${}_{1-x}$Te${}_{x}$ bulk samples [210] are also shown, for comparison.

**Figure 8.**Relation between ${T}_{\mathrm{c}}$ and (

**a**) bond angle, $\alpha $; and (

**b**) Chalcogen height, h, for FeSe${}_{1-x}$Te${}_{x}$ films on LaAlO${}_{3}$ (red symbols) and CaF${}_{2}$ (blue symbols) substrates. The data for FeSe${}_{1-x}$Te${}_{x}$ bulk samples [210] are also shown, for comparison. The open (closed) symbols corresponds to the samples with (without) structural transitions.

**Table 1.**In-plane lattice parameters, ${a}_{\mathrm{sub}}$, and coefficients of thermal expansion at 300 K, ${\alpha}_{300\mathrm{K}}$, for substrate materials.

Substrate Material | ${\mathit{a}}_{\mathbf{sub}}$ ( Å ) | ${\mathit{\alpha}}_{300\mathrm{K}}$ ($\times {10}^{-6}$ 1/K) |
---|---|---|

Yttria stabilized zirconia (Y:ZrO${}_{2}$) | 3.635 ($a/\sqrt{2}$) [170] | 11 [171] |

YAlO${}_{3}$ (YAO) | 3.716 ($a/\sqrt{2}$) [172] | 3.8 [173] |

LaSrAlO${}_{4}$ (LSAO) | 3.754 [174] | 7.55 [175] |

LaAlO${}_{3}$ (LAO) | 3.793 ($a/\sqrt{2}$) [176] | 5.77 [177] |

LaSrGaO${}_{4}$ (LSGO) | 3.844 [178] | 10.05 [179] |

(La,Sr)(Al,Ta)O${}_{3}$ (LSAT) | 3.869 ($a/\sqrt{2}$) [180] | 8.22 [177] |

SrTiO${}_{3}$ (STO) | 3.905 [181] | 10.3 [182] |

MgO | 4.211 [183] | 10.5 [182] |

CaF${}_{2}$ | 3.865 ($a/\sqrt{2}$) [184] | 18.9 [185] |

SrF${}_{2}$ | 4.101 ($a/\sqrt{2}$) [186] | 18.1 [185] |

BaF${}_{2}$ | 4.382 ($a/\sqrt{2}$) [187] | 18.4 [185] |

GaAs | 3.997 ($a/\sqrt{2}$) [188] | 5.7 [182] |

Atom | ${\mathit{x}}_{\mathit{atom}}$ | ${\mathit{y}}_{\mathit{atom}}$ | ${\mathit{z}}_{\mathit{atom}}$ | Occupancy |
---|---|---|---|---|

Fe | 0.75 | 0.25 | 0 | 1 |

$\mathrm{Se}/\mathrm{Te}$ | 0.25 | 0.25 | ${z}_{Ch}$ | $1-x/x$ |

**Table 3.**Summary of the estimation for structural parameters in FeSe${}_{1-x}$Te${}_{x}$ films by the XRD simulation.

x | Substrate | a (Å) | c (Å) | ${\mathit{r}}_{\mathbf{exp}}$ | ${\mathit{z}}_{\mathit{Ch}}$ | $\mathit{\alpha}$ (deg.) | h (Å) |
---|---|---|---|---|---|---|---|

0 | CaF${}_{2}$ | 3.735 | 5.584 | 2.410 | 0.239 | 108.80 | 1.337 |

0.1 | CaF${}_{2}$ | 3.756 | 5.632 | 1.665 | 0.240 | 108.61 | 1.349 |

0.2 | CaF${}_{2}$ | 3.722 | 5.755 | 2.215 | 0.249 | 104.80 | 1.433 |

0.3 | CaF${}_{2}$ | 3.748 | 5.869 | 1.592 | 0.248 | 104.35 | 1.455 |

0.4 | CaF${}_{2}$ | 3.758 | 5.758 | 1.733 | 0.253 | 103.33 | 1.486 |

0.5 | CaF${}_{2}$ | 3.771 | 5.996 | 1.483 | 0.254 | 102.24 | 1.520 |

0.6 | CaF${}_{2}$ | 3.752 | 6.066 | 1.477 | 0.256 | 100.70 | 1.555 |

0.7 | CaF${}_{2}$ | 3.755 | 6.132 | 1.143 | 0.255 | 100.47 | 1.562 |

0 | LaAlO${}_{3}$ | 3.750 | 5.530 | 1.137 | 0.228 | 112.10 | 1.262 |

0.1 | LaAlO${}_{3}$ | 3.779 | 5.558 | 2.383 | 0.245 | 108.46 | 1.361 |

0.3 | LaAlO${}_{3}$ | 3.776 | 5.815 | 2.658 | 0.256 | 103.39 | 1.491 |

0.4 | LaAlO${}_{3}$ | 3.734 | 5.883 | 1.848 | 0.254 | 102.66 | 1.494 |

0.5 | LaAlO${}_{3}$ | 3.789 | 5.977 | 1.748 | 0.256 | 102.10 | 1.531 |

0.6 | LaAlO${}_{3}$ | 3.770 | 6.042 | 1.267 | 0.254 | 101.71 | 1.534 |

0.7 | LaAlO${}_{3}$ | 3.797 | 6.126 | 1.201 | 0.256 | 100.98 | 1.565 |

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Imai, Y.; Nabeshima, F.; Maeda, A.
Comparative Review on Thin Film Growth of Iron-Based Superconductors. *Condens. Matter* **2017**, *2*, 25.
https://doi.org/10.3390/condmat2030025

**AMA Style**

Imai Y, Nabeshima F, Maeda A.
Comparative Review on Thin Film Growth of Iron-Based Superconductors. *Condensed Matter*. 2017; 2(3):25.
https://doi.org/10.3390/condmat2030025

**Chicago/Turabian Style**

Imai, Yoshinori, Fuyuki Nabeshima, and Atsutaka Maeda.
2017. "Comparative Review on Thin Film Growth of Iron-Based Superconductors" *Condensed Matter* 2, no. 3: 25.
https://doi.org/10.3390/condmat2030025