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Nonvolatile Isomorphic Valence Transition in SmTe Films.

ABSTRACT: The burgeoning field of optoelectronic devices necessitates a mechanism that gives rise to a large contrast in the electrical and optical properties. A SmTe film with a NaCl-type structure demonstrates significant differences in resistivity (over 10⁵) and band gap (approximately 1.45 eV) between as-deposited and annealed films, even in the absence of a structural transition. The change in the electronic structure and accompanying physical properties is attributed to a rigid-band shift triggered by a valence transition (VT) between Sm²⁺ and Sm³⁺. The stress field within the SmTe film appears closely tied to the mixed valence state of Sm, suggesting that stress is a driving force in this VT. By mixing the valence states, the formation energy of the low-resistive state decreases, providing nonvolatility. Moreover, the valence state of Sm can be regulated through annealing and device-operation processes, such as applying voltage and current pulses. This investigation introduces an approach to developing semiconductor materials for optoelectrical applications.

SUBMITTER: Hatayama S

PROVIDER: S-EPMC10832057 | biostudies-literature | 2024 Jan

REPOSITORIES: biostudies-literature

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Nonvolatile Isomorphic Valence Transition in SmTe Films.

Hatayama Shogo S Mori Shunsuke S Saito Yuta Y Fons Paul J PJ Shuang Yi Y Sutou Yuji Y

ACS nano 20240116 4

The burgeoning field of optoelectronic devices necessitates a mechanism that gives rise to a large contrast in the electrical and optical properties. A SmTe film with a NaCl-type structure demonstrates significant differences in resistivity (over 10<sup>5</sup>) and band gap (approximately 1.45 eV) between as-deposited and annealed films, even in the absence of a structural transition. The change in the electronic structure and accompanying physical properties is attributed to a rigid-band shift ...[more]

PMID: 38228321

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Project description:A temperature induced valence phase transition from Yb3+ at higher temperatures to Yb2+ at lower temperatures was observed at T = 110(1) K for intermetallic YbPd2Al3. The title compound has been prepared from the elements in sealed tantalum ampoules. The structure was refined from single-crystal data and the title compound was found to crystallize in the hexagonal YNi2Al3 type structure with space group P6/mmm and lattice parameters of a = 929.56(7) and c = 420.16(3) pm (300 K data). Full ordering of the Pd and Al atoms within the [Pd2Al3] δ- polyanion was observed. Magnetic measurements revealed an anomaly in the dc susceptibility data and intermediate valent Yb at higher temperature, as observed from the effective magnetic moment. The proposed valence phase transition was also observed as a λ-type anomaly in heat capacity measurements (T = 108.4(1) K), however, no systematic shift of the λ-peak was observed in field dependent heat capacity measurements. An antiferromagnetic ordering at this temperature, however, could be excluded, based on field-dependent susceptibility measurements and magnetization isotherms. No dynamic phenomenon was observed in ac susceptibility measurements, excluding e.g. spin-glass behavior. Subsequent temperature dependent single-crystal and powder X-ray diffraction experiments indicated a steep increase in the length of the c axis around T = 110 K upon cooling. However, no structural phase transition was found via single-crystal diffraction experiments conducted at 90 K. The anomaly was also observed in other physical measurements of e.g. the electrical resistivity, indicating a clear change in the electronic structure of the material. X-ray photoelectron spectroscopy conducted at room temperature shows the presence of both, Yb2+ and Yb3+, underlining the mixed-valent state. Members of the solid solution Yb1-x Ca x Pd2Al3 (x = 0.33, 0.67, 1) were finally used to further study the charge ordering and the present temperature induced valence phase transition.

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Nonvolatile Isomorphic Valence Transition in SmTe Films.

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Nonvolatile Isomorphic Valence Transition in SmTe Films.

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