Phase Equilibria in the Ag–Ge–Bi–Te System and Thermodynamic Properties of the nGeTe×mBi2Te3 (n, m = 1-4) Layered Compounds

Mykola Moroz*, Fiseha Tesfaye, Pavlo Demchenko, Myroslava Prokhorenko, Orest Pereviznyk, Bohdan Rudyk, Lyudmyla Soliak, Daniel Lindberg, Oleksandr Reshetnyak, Leena Hupa

*Corresponding author for this work

Research output: Chapter in Book/Conference proceedingConference contributionScientificpeer-review

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Abstract

Phase equilibria of the Ag–Ge–Bi–Te system in the part GeTe–Ag 8GeTe 6–Te–Bi 2Te 3 (I) were established by the electromotive force (EMF) method with a solid Ag + conducting electrolyte. It was shown that the concentration space of (I) in the part 4GeTe⋅Bi 2Te 3–Ag 8GeTe 6–Te–Bi 2Te consists of 8 four-phase regions, formed of the layered compounds of the nGeTe⋅mBi 2Te 3 (n, m = 1–4) homologous range, as well as Ag 8GeTe 6, Bi 2Te 3, and Te. Equations of overall potential-forming reaction of the decomposition and synthesis of compounds of the homologous range were written for each region. Reactions were performed in the following electrochemical cells (ECCs) (−)IE | Ag | SE | PE | IE(+), where IE is the inert electrode (graphite), Ag is the negative (left) electrode, SE is the solid-state Ag + ion-conducting electrolyte, PE is the positive (right) electrode. PEs of ECCs were prepared by melting of a mixture of the high-purity elements Ag, Ge, Bi, and Te. The component ratios in samples were determined based on the equations of the potential-forming reactions in respective phase Phase equilibria regions. The finely grounded samples were used as PEs of ECCs. The synthesis of an equilibrium set of phases was performed in the part of PE that is in contact with SE of ECC at T = 580 K for 50 h. Silver cations that shift from the left to the right electrode acted as the nucleation centers of equilibrium compounds in the corresponding phase regions. Linear dependences E versus T of ECCs in the range of T = (440–500) K were used to calculate values of the Gibbs energies, enthalpies of formation, and entropies of compounds GeTe⋅4Bi 2Te 3, GeTe⋅3Bi 2Te 3, GeTe⋅2.5Bi 2Te 3, GeTe⋅2Bi 2Te 3, GeTe⋅Bi 2Te 3, 2GeTe⋅Bi 2Te 3, 3GeTe⋅Bi 2Te 3, and 4GeTe⋅Bi 2Te 3. The differences in the values of the thermodynamic functions of GeTe-rich and Bi 2Te 3-rich compounds with respect to GeTe⋅Bi 2Te 3 correlate well with the literature data on the differences of their crystal structures.

Original languageEnglish
Title of host publicationTMS 2022 151st Annual Meeting and Exhibition Supplemental Proceedings
Place of PublicationSwitzerland AG
PublisherSpringer International Publishing
Chapter7
Pages60-73
Number of pages14
Volume1
Edition1
ISBN (Electronic)978-3-030-92381-5
ISBN (Print)978-3-030-92381-5, 978-3-030-92381-5, 978-3-030-92381-5, 978-3-030-92380-8
DOIs
Publication statusPublished - 1 Jan 2022
MoE publication typeA4 Article in a conference publication
EventTMS 2022 Annual Meeting & Exhibition - Anaheim Convention Center & Anaheim Marriott , Anaheim, United States
Duration: 27 Feb 20223 Mar 2022
Conference number: 151
https://www.tms.org/AnnualMeeting/TMS2022

Publication series

NameMinerals, Metals and Materials Series
ISSN (Print)2367-1181
ISSN (Electronic)2367-1696

Conference

ConferenceTMS 2022 Annual Meeting & Exhibition
Abbreviated titleTMS2022
Country/TerritoryUnited States
CityAnaheim
Period27/02/2203/03/22
Internet address

Keywords

  • Layered Compounds
  • Phase equilibria
  • Thermodynamic properties
  • EMF method
  • Gibbs energy

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