Pressure-induced transformations in α- and β-Ge 3N4: In situ studies by synchrotron X-ray diffraction

Emmanuel Soignard, Paul F. McMillan, Clivia Hejny, Kurt Leinenweber

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

Metastable high-pressure transformations in germanium nitride (α- and β-Ge3N4 polymorphs) have been studied by energy- and angle-dispersive synchrotron X-ray diffraction at high pressures in a diamond anvil cell. Between P=22 and 25GPa, the phenacite-structured β-Ge3N4 phase (P63/m) undergoes a 7% reduction in unit-cell volume. The densification is primarily concerned with the a-axis parameter, in a plane normal to the hexagonal c-axis. Based on results of previous LDA calculations and Raman spectroscopic studies, we propose that the structural collapse is due to transformation into a new metastable polymorph (δ-Ge3N4) that has a unit-cell symmetry based upon P3, that is related to the low-pressure β-Ge 3N4 phase by concerted displacements of N atoms away from special symmetry sites in the plane normal to the c-axis. No such transformation occurs for α-Ge3N4, due to the different stacking of linked GeN4 layers. All three polymorphs (α-, β- and δ-Ge3N4) are based on tetrahedrally coordinated Ge atoms, unlike the spinel-structured γ-Ge 3N4 phase, that contains octahedrally coordinated Ge 4+. Experimentally determined bulk modulus values for α-Ge 3N4 (K0=165(10) GPa, K0′=3. 7(4)) and β-Ge3N4 (K0=185(7) GPa, K 0′=4.4(5)) are in excellent agreement with theoretical predictions. The bulk modulus for the new δ-Ge3N4 polymorph is only determined above the β-δ transition pressure (P=24GPa); K=161(20) GPa, assuming K′=4. Above 45GPa, both α- and δ-Ge3N4 polymorphs become amorphous, as determined by X-ray diffraction and Raman scattering.

Original languageEnglish (US)
Pages (from-to)299-311
Number of pages13
JournalJournal of Solid State Chemistry
Volume177
Issue number1
DOIs
StatePublished - Jan 1 2004

Fingerprint

Polymorphism
Synchrotrons
synchrotrons
bulk modulus
X ray diffraction
cells
diffraction
x rays
transition pressure
symmetry
densification
anvils
Elastic moduli
spinel
nitrides
atoms
germanium
Germanium
low pressure
Atoms

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Cite this

Pressure-induced transformations in α- and β-Ge 3N4 : In situ studies by synchrotron X-ray diffraction. / Soignard, Emmanuel; McMillan, Paul F.; Hejny, Clivia; Leinenweber, Kurt.

In: Journal of Solid State Chemistry, Vol. 177, No. 1, 01.01.2004, p. 299-311.

Research output: Contribution to journalArticle

@article{e092652a5df947f29d7b3a06b490128f,
title = "Pressure-induced transformations in α- and β-Ge 3N4: In situ studies by synchrotron X-ray diffraction",
abstract = "Metastable high-pressure transformations in germanium nitride (α- and β-Ge3N4 polymorphs) have been studied by energy- and angle-dispersive synchrotron X-ray diffraction at high pressures in a diamond anvil cell. Between P=22 and 25GPa, the phenacite-structured β-Ge3N4 phase (P63/m) undergoes a 7{\%} reduction in unit-cell volume. The densification is primarily concerned with the a-axis parameter, in a plane normal to the hexagonal c-axis. Based on results of previous LDA calculations and Raman spectroscopic studies, we propose that the structural collapse is due to transformation into a new metastable polymorph (δ-Ge3N4) that has a unit-cell symmetry based upon P3, that is related to the low-pressure β-Ge 3N4 phase by concerted displacements of N atoms away from special symmetry sites in the plane normal to the c-axis. No such transformation occurs for α-Ge3N4, due to the different stacking of linked GeN4 layers. All three polymorphs (α-, β- and δ-Ge3N4) are based on tetrahedrally coordinated Ge atoms, unlike the spinel-structured γ-Ge 3N4 phase, that contains octahedrally coordinated Ge 4+. Experimentally determined bulk modulus values for α-Ge 3N4 (K0=165(10) GPa, K0′=3. 7(4)) and β-Ge3N4 (K0=185(7) GPa, K 0′=4.4(5)) are in excellent agreement with theoretical predictions. The bulk modulus for the new δ-Ge3N4 polymorph is only determined above the β-δ transition pressure (P=24GPa); K=161(20) GPa, assuming K′=4. Above 45GPa, both α- and δ-Ge3N4 polymorphs become amorphous, as determined by X-ray diffraction and Raman scattering.",
author = "Emmanuel Soignard and McMillan, {Paul F.} and Clivia Hejny and Kurt Leinenweber",
year = "2004",
month = "1",
day = "1",
doi = "10.1016/j.jssc.2003.08.021",
language = "English (US)",
volume = "177",
pages = "299--311",
journal = "Journal of Solid State Chemistry",
issn = "0022-4596",
publisher = "Academic Press Inc.",
number = "1",

}

TY - JOUR

T1 - Pressure-induced transformations in α- and β-Ge 3N4

T2 - In situ studies by synchrotron X-ray diffraction

AU - Soignard, Emmanuel

AU - McMillan, Paul F.

AU - Hejny, Clivia

AU - Leinenweber, Kurt

PY - 2004/1/1

Y1 - 2004/1/1

N2 - Metastable high-pressure transformations in germanium nitride (α- and β-Ge3N4 polymorphs) have been studied by energy- and angle-dispersive synchrotron X-ray diffraction at high pressures in a diamond anvil cell. Between P=22 and 25GPa, the phenacite-structured β-Ge3N4 phase (P63/m) undergoes a 7% reduction in unit-cell volume. The densification is primarily concerned with the a-axis parameter, in a plane normal to the hexagonal c-axis. Based on results of previous LDA calculations and Raman spectroscopic studies, we propose that the structural collapse is due to transformation into a new metastable polymorph (δ-Ge3N4) that has a unit-cell symmetry based upon P3, that is related to the low-pressure β-Ge 3N4 phase by concerted displacements of N atoms away from special symmetry sites in the plane normal to the c-axis. No such transformation occurs for α-Ge3N4, due to the different stacking of linked GeN4 layers. All three polymorphs (α-, β- and δ-Ge3N4) are based on tetrahedrally coordinated Ge atoms, unlike the spinel-structured γ-Ge 3N4 phase, that contains octahedrally coordinated Ge 4+. Experimentally determined bulk modulus values for α-Ge 3N4 (K0=165(10) GPa, K0′=3. 7(4)) and β-Ge3N4 (K0=185(7) GPa, K 0′=4.4(5)) are in excellent agreement with theoretical predictions. The bulk modulus for the new δ-Ge3N4 polymorph is only determined above the β-δ transition pressure (P=24GPa); K=161(20) GPa, assuming K′=4. Above 45GPa, both α- and δ-Ge3N4 polymorphs become amorphous, as determined by X-ray diffraction and Raman scattering.

AB - Metastable high-pressure transformations in germanium nitride (α- and β-Ge3N4 polymorphs) have been studied by energy- and angle-dispersive synchrotron X-ray diffraction at high pressures in a diamond anvil cell. Between P=22 and 25GPa, the phenacite-structured β-Ge3N4 phase (P63/m) undergoes a 7% reduction in unit-cell volume. The densification is primarily concerned with the a-axis parameter, in a plane normal to the hexagonal c-axis. Based on results of previous LDA calculations and Raman spectroscopic studies, we propose that the structural collapse is due to transformation into a new metastable polymorph (δ-Ge3N4) that has a unit-cell symmetry based upon P3, that is related to the low-pressure β-Ge 3N4 phase by concerted displacements of N atoms away from special symmetry sites in the plane normal to the c-axis. No such transformation occurs for α-Ge3N4, due to the different stacking of linked GeN4 layers. All three polymorphs (α-, β- and δ-Ge3N4) are based on tetrahedrally coordinated Ge atoms, unlike the spinel-structured γ-Ge 3N4 phase, that contains octahedrally coordinated Ge 4+. Experimentally determined bulk modulus values for α-Ge 3N4 (K0=165(10) GPa, K0′=3. 7(4)) and β-Ge3N4 (K0=185(7) GPa, K 0′=4.4(5)) are in excellent agreement with theoretical predictions. The bulk modulus for the new δ-Ge3N4 polymorph is only determined above the β-δ transition pressure (P=24GPa); K=161(20) GPa, assuming K′=4. Above 45GPa, both α- and δ-Ge3N4 polymorphs become amorphous, as determined by X-ray diffraction and Raman scattering.

UR - http://www.scopus.com/inward/record.url?scp=0347761432&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0347761432&partnerID=8YFLogxK

U2 - 10.1016/j.jssc.2003.08.021

DO - 10.1016/j.jssc.2003.08.021

M3 - Article

AN - SCOPUS:0347761432

VL - 177

SP - 299

EP - 311

JO - Journal of Solid State Chemistry

JF - Journal of Solid State Chemistry

SN - 0022-4596

IS - 1

ER -