New Low‐Energy Crystal Structures in ZrO<sub>2</sub> and HfO<sub>2</sub>

Kersch, Alfred; Falkowski, Max

doi:10.1002/pssr.202100074

Cited by 18 publications

(9 citation statements)

References 26 publications

(30 reference statements)

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“…29 structures. [ 6,7 ] The oIII no. 29 can be considered to contain two polar oxygen pairs and two nonpolar oxygen pairs in spacer position, relative to the perturbed cubic lattice of metal ions.…”

Section: Resultsmentioning

confidence: 99%

“…HfO 2 and ZrO 2 with their metastable but polar and ferroelectric

P c a 2_{1}

phase are materials that possess excellent properties for microelectronic and technical applications, [ 1 ] which range from dense nonvolatile memories [ 2,3 ] over thin‐film piezoelectric transducers [ 4 ] to thin‐film pyroelectric devices. [ 5 ] The polymorphism of the phases in HfO 2 and ZrO 2 is still surprising as new relevant phases have been found only recently by simulations, [ 6–8 ] and some experimental findings are still not consistent with the conventionally considered phases, [ 9 ] which are the monoclinic ground‐state m ‐phase ( P2 1 /c , no. 14), the polar‐orthorhombic o III‐phase ( Pca2 1 , no.…”

Section: Introductionmentioning

confidence: 99%

“…61), which recently have been distinguished theoretically and experimentally. [6,7] The list is completed with the recently identified orthorhombic oV-phase (Pnma, no. 62) that is inequivalent to the energetically unfavorable oII-phase (Pnma, no.…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of Low‐Energy Phases of Hafnia and Zirconia from Density Functional Theory Calculations

Antunes

Ganser

Kuenneth

et al. 2022

Physica Rapid Research Ltrs

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A systematic simulation study of low‐energy phases of HfO2 and ZrO2, including 24‐atomic cells derived from 180° interphases, leads to a new monoclinic Pc phase (mIII) with a monoclinic angle and a polarization of 0.3 C m−2. This opens up a new transition path toward the monoclinic P2 1 /c phase (m) starting from the tetragonal P4 2 /nmc phase (t), with comparable lower‐energy barriers, where the high‐symmetric phases show the largest temperature dependence. The tetragonal P4 2 /nmc phase, the cubic (c) phase, and the less investigated cubic (cII) phase are favored.

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Section: Resultsmentioning

confidence: 99%

“…HfO 2 and ZrO 2 with their metastable but polar and ferroelectric

P c a 2_{1}

Section: Introductionmentioning

confidence: 99%

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Characteristics of Low‐Energy Phases of Hafnia and Zirconia from Density Functional Theory Calculations

Antunes

Ganser

Kuenneth

et al. 2022

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“…First, orthorhombic Pbca could potentially contribute to the observed antiferroelectric behavior in ZrO 2 , [ 37 ] as this phase is a combination of two unit cells of the polar o ‐phase with opposite polarizations. [ 22,38,39 ] This phase is also found to be energetically close to the ground state m ‐phase. [ 39,40 ] Additionally, the t ‐phase has been identified as a potential driver of antiferroelectric behavior in ZrO 2 polycrystalline thin films [ 41 ] ; this has been explained as a transition from the nonpolar t ‐phase to the polar o ‐phase.…”

Section: Introductionmentioning

confidence: 82%

Ferroelectricity in Epitaxial Tetragonal ZrO₂Thin Films

El Boutaybi,

Maroutian,

Largeau

et al. 2023

Adv Elect Materials

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The crystal structure and ferroelectric properties of epitaxial ZrO2 films ranging from 7 to 42 nm thickness grown on La0.67Sr0.33MnO3 buffered (110)‐oriented SrTiO3 substrate are reported. By employing X‐ray diffraction, a tetragonal phase (t‐phase) at all investigated thicknesses, with slight in‐plane strain due to the substrate in the thinnest films, is confirmed. Further confirmation of the t‐phase is obtained through infrared absorption spectroscopy with synchrotron light, performed on ZrO2 membrane transferred onto a high resistive silicon substrate. Up to a thickness of 31 nm, the ZrO2 epitaxial films exhibit ferroelectric behavior, at variance with the antiferroelectric behavior reported previously for the t‐phase in polycrystalline films. However, the ferroelectricity is found here to diminish with increasing film thickness, with a polarization of 13 µC cm−2 and down to 1 µC cm−2 for 7 and 31 nm thick ZrO2 films, respectively. Given that the t‐phase is nonpolar, the observations emphasize the influence of external factors, in promoting polarization in t‐ZrO2 thin films. These findings provide new insights into the ferroelectric properties and structure of ZrO2 thin films, and open up new directions to investigate the origin of ferroelectricity in ZrO2 and to optimize this material for future applications.

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“…Several phases were reported to be present or coexisting in doped HfO 2 or ZrO 2 films ranging from monoclinic (space group P2 1 /c), tetragonal (P4 2 /nmc), cubic ( 3 Fm m ), rhombohedral (R3m), and different orthorhombic phases that can be nonpolar (Pnma), antipolar (Pbca), nonpolar (Pbca), or polar (Pca2 1 ). [5,6] A remarkable property of the material is the phase coexistence between the nonpolar tetragonal and polar orthorhombic phase. The conditions of this phase coexistence are little investigated because the participating phases have very similar structural properties, and the investigation requires correlated measurement of film properties like the remanent polarization and the dielectric constant.…”

Section: Temperature-dependent Phase Transitions In Hf X Zr 1-x O 2 M...mentioning

confidence: 99%

Temperature‐Dependent Phase Transitions in Hf_xZr_1‐xO₂ Mixed Oxides: Indications of a Proper Ferroelectric Material

Schroeder

Mittmann

Materano

et al. 2022

Adv Elect Materials

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Knowledge about phase transitions in doped HfO2 and ZrO2‐based films is crucial for developing future ferroelectric devices. These devices should perform in ambient temperature ranges with no degradation of device performance. Here, the phase transition from the polar orthorhombic to the nonpolar tetragonal phase in thin films is of significant interest. Detailed electrical and structural characterization is performed on 10 nm mixed HfxZr1‐xO2 binary oxides with different ZrO2 in HfO2 and small changes in oxygen content. Both dopant and oxygen content directly impact the phase transition temperature between the polar and nonpolar phase. A first‐order phase transition with thermal hysteresis is observed from the nonpolar to the polar phase with a maximum in the dielectric constant. The observed phase transition temperatures confirm trends as obtained by DFT calculations. Based on the outcome of the measurements, the classification of the ferroelectric material is discussed.

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New Low‐Energy Crystal Structures in ZrO₂ and HfO₂

Abstract: From first principles, the energy and volume of metastable phases of ZrO 2 and HfO 2 are calculated. At low energy, two inequivalent, nonpolar, orthorhombic phases of the same space group Pbca number P61 are found.

Cited by 18 publications

References 26 publications

Characteristics of Low‐Energy Phases of Hafnia and Zirconia from Density Functional Theory Calculations

Characteristics of Low‐Energy Phases of Hafnia and Zirconia from Density Functional Theory Calculations

Ferroelectricity in Epitaxial Tetragonal ZrO₂Thin Films

Temperature‐Dependent Phase Transitions in Hf_xZr_1‐xO₂ Mixed Oxides: Indications of a Proper Ferroelectric Material

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New Low‐Energy Crystal Structures in ZrO2 and HfO2

Abstract: From first principles, the energy and volume of metastable phases of ZrO 2 and HfO 2 are calculated. At low energy, two inequivalent, nonpolar, orthorhombic phases of the same space group Pbca number P61 are found.

Cited by 18 publications

References 26 publications

Characteristics of Low‐Energy Phases of Hafnia and Zirconia from Density Functional Theory Calculations

Characteristics of Low‐Energy Phases of Hafnia and Zirconia from Density Functional Theory Calculations

Ferroelectricity in Epitaxial Tetragonal ZrO2Thin Films

Temperature‐Dependent Phase Transitions in HfxZr1‐xO2 Mixed Oxides: Indications of a Proper Ferroelectric Material

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Product

Resources

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New Low‐Energy Crystal Structures in ZrO₂ and HfO₂

Ferroelectricity in Epitaxial Tetragonal ZrO₂Thin Films

Temperature‐Dependent Phase Transitions in Hf_xZr_1‐xO₂ Mixed Oxides: Indications of a Proper Ferroelectric Material