Influence of crystallite size and composition on the formation of polarons in nanocrystalline tungstates

Project leader Georgijs Bakradze

Agreement No 1.1.1.2/16/I/001

Research application No. 1.1.1.2/VIAA/3/19/444

Tungstates represent a large class of materials with a wide range of applications, including but not limited to scintillators, solid-state laser hosts, photocatalysis, supercapacitors, lithium-ion batteries and sensors. Many properties of tungstates are governed by the physics of lattice defects. Among them, the formation of polarons in tungstates has been rarely studied but is important for tailoring their optical and electrical properties. Within this project we intend to conduct systematic investigations of the local atomic and electronic structure in nanocrystalline tungstates with a particular emphasis on the local lattice deformations induced by the formation of the polaronic centres and their dependence on the crystallite size, dimensionality and chemical composition. This challenging task will be addressed using state-of-the-art experimental synchrotron-based techniques such as X-ray absorption spectroscopy (XAS) and resonant X-ray emission spectroscopy (RXES) in combination with theoretical analysis based on the first principles and atomistic simulations. A comprehensive understanding of the interconnection between the properties and defect physics in nanocrystalline tungstates will contribute substantially to the improvement of their functional properties in demanding applications.

The project will be implemented at the Institute of Solid State Physics, University of Latvia from 01.01.2020 until 31.12.2022. The total cost of the project is 133’805.88 EUR.

Project news

02.01.2023.

In the end of the year two scientific papers have been published:

1) “Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates” was published in the Journal of Physics and Chemistry of Solids:

G. Bakradze, E. Welter, A. Kuzmin,

Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates,

J. Phys. Chem. Solids 172 (2023) 111052.

Doi: 10.1016/j.jpcs.2022.111052.

2) "Octahedral Tilting in Homologous Perovskite Series CaMoO₃-SrMoO₃- BaMoO₃ Probed by Temperature-Dependent EXAFS Spectroscopy" was published in the journal Materials:

G. Bakradze, A. Kuzmin,

Octahedral tilting in homologous perovskites series CaMoO3-SrMoO3-BaMoO3 probed by temperature-dependent EXAFS spectroscopy,

Materials 15 (2022) 7619.

Doi: 10.3390/ma15217619.

01.10.2022.

During the implementation of this project, we were able to synthesize and characterize two new single-phase materials based on tungstates. These materials belong to a relatively new class of materials - the so-called medium and high entropy materials (in this particular case, tungstates), in which, respectively, four (medium entropy) and five (high entropy) different elements are incorporated in one crystalline sublattice. A paper entitled “Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates” has been submitted for publication in the Journal of Physics and Chemistry of Solids.

In parallel, a new way to analyze RMC data - a polyhedral analysis - has been developed and applied to characterize perovskites of alkaline earth metals (CaMoO₃, SrMoO₃, and BaMoO₃), as described in the article devoted to the peculiarities of their local structures. "Octahedral Tilting in Homologous Perovskite Series CaMoO₃-SrMoO₃- BaMoO₃ Probed by Temperature-Dependent EXAFS Spectroscopy" submitted for publication in the journal Materials.

07.07.2022.

During the last months, we worked on the analysis of the experimental data and their description in the manuscripts. Manuscripts have been written on:

1. new materials: high and medium entropy tungstates and their local structure,
2. on the effect of protonation on the local structure of tungstates,
3. on the peculiarities of CaMoO₃, CaMoO₄, SrMoO₃, SrMoO₄, BaMoO₃, BaMoO₄ and their local structures.

02.05.2022.

Using co-precipitation and solid-state synthesis methods we have synthesized the following samples (high-entropy tungstate, CaMoO₃, CaMoO₄, SrMoO₃, SrMoO₄, BaMoO₃, BaMoO₄, RE-doped SrMoO₄ and CdMoO₄). The samples were analyzed using in-house techniques (X-ray diffraction analysis and Raman spectroscopy), as well as X-ray absorption spectroscopy. The XAS measurements were performed in February-March during another visit at the HASYLAB/DESY PETRA-III synchrotron centre at PETRA-III P64 work station.

11.01.2022.

During the last report period the following paper has been published:

G. Bakradze, A. Kalinko, A. Kuzmin,
Chemical-state analyses of Ni, Zn, and W ions in NiWO4–ZnWO4 solid solutions by X-ray photoelectron spectroscopy,
J Phys Chem Solids 161 (2022) 110425.
DOI: 10.1016/j.jpcs.2021.110425

From 22nd till 26th November 2021, the 9th International Conference on Actual Problems in Solid State Physics was held at the Academy of Sciences in Minsk, Belarus. In this conference we reported our results as a poster presentation “Changes of chemical states of Ni, Zn, and W ions in NiWO4 upon doping with ZnWO4: an X-ray photoelectron spectroscopy study”.

At the end of the year, the results obtained within this project have been recognized by the Latvian Academy of Sciences as one of the most significant scientific achievements in Latvia in 2021.

01.09.2021.

During the last report period a paper entitled “Evidence of nickel ions dimerization in NiWO₄ and NiWO₄-ZnWO₄ solid solutions probed by EXAFS spectroscopy and reverse Monte Carlo simulations” has been published in Acta Materialia:

G. Bakradze, A. Kalinko, A. Kuzmin,
Evidence of dimerization of nickel ions in NiWO₄ and Zn_cNi_1-cWO₄ solid solutions probed by EXAFS spectroscopy and reverse Monte Carlo simulations,
Acta Mater. 217 (2021) 117171.
DOI: 10.1016/j.actamat.2021.117171

From the 11th-16th July 2021 the 18th International Conference on X-Ray Absorption Fine Structure 2021 (XAFS21) was held at the University of Sydney, Australia. In this conference we reported our results as an oral presentation “Dimerization of nickel ions in ZnWO₄-NiWO₄ solid solutions as-evidenced by EXAFS spectroscopy”.

A research project for synchrotron measurements for Spring 2022 at the HASYLAB/DESY PETRA-III synchrotron centre has been written and submitted.

02.07.2021.

During the last report period we have written two papers on x-ray absorption spectroscopy and x-ray photoelectron spectroscopy of Zn_cNi_1-cWO₄ (c=0.0-1.0) solid solutions.

A manuscript entitled “Evidence of nickel ions dimerization in NiWO₄ and NiWO₄-ZnWO₄ solid solutions probed by EXAFS spectroscopy and reverse Monte Carlo simulations” deals with an interesting observation: nickel ions form dimers within quasi-one-dimentional [NiO₆] chains. Our observation is very surprising, because NiWO₄ is a well-known material. A manuscript entitled “Chemical-state analyses of Ni, Zn, and W ions in NiWO₄-ZnWO₄ solid solutions by x-ray photoelectron spectroscopy” discusses the x-ray photoelectron spectroscopy measurements performed on Zn_cNi_1-cWO₄ (c=0.0-1.0) solid solutions.

In the end of May - beginning of June, the post-doctoral researcher has participated in an eight-day HERCULES Specialized Course 2021 devoted to the multi-technique approach of CERIC-ERIC as a tool for Nanoscience.

A research project for synchrotron measurements for Autumn 2021 at the HASYLAB/DESY PETRA-III synchrotron centre has been written and submitted.

08.04.2021.

During the last report period we have combined and analyzed the data on x-ray absorption spectroscopy and x-ray photoelectron spectroscopy of Zn_cNi_1-cWO₄ (c=0.0-1.0) solid solutions. These analyses will be published in two scientific papers.

In January and February, the results of the current research were presented at the annual DESY Photon Science User Meeting and LU CFI 37. Scientific Conference.

01.01.2021.

A paper entitled “X-ray absorption and Raman spectroscopy studies of tungstates solid solutions Zn_cNi_1-cWO₄ (c=0.0-1.0)” has been published in the journal “Low Temperature Physics”: Bakradze et al, Low Temperature Physics 46 (2020) 1412.

Measurements of scheelite samples using resonant X-ray emission spectroscopy and  X-ray absorption spectroscopy have been performed at the HASYLAB/DESY PETRA-III synchrotron centre at P64 and P65 work station, respectively.

Two online workshops have been attended. The first one was a three-days workshop entitled "PETRA-IV: Technical Challenges and Scientific Computing" was organised by the HASYLAB/DESY PETRA-III synchrotron centre in Hamburg. The second one was a four-days workshop entitled “Advanced XAS Data Analysis and Modeling Workshop” was organized by the Canadian Light Source in Saskatchewan.

01.10.2020.

A paper entitled “X-ray absorption and Raman spectroscopy studies of tungstates solid solutions Zn_cNi_1-cWO₄ (c=0.0-1.0)” has been accepted for publication in the journal “Low Temperature Physics”.

Nd₂(WO₄)₃, CaWO₄, SrWO₄, BaWO₄, and PbWO₄ samples were synthesized and analyzed: their purity was confirmed by X-ray diffraction analysis and X-ray photoelectron spectroscopy.  Their X-ray absorption spectroscopy measurements have been performed between 09.09.2020. and 14.09.2020. at the HASYLAB/DESY PETRA-III synchrotron centre at PETRA-III P65 work station.

An online seminar - organised by the ESRF synchrotron in Grenoble - "X-ray absorption spectroscopy for solving chemical problems" (September 18) has been attended.

A research project for synchrotron measurements for Spring 2021 at the HASYLAB/DESY PETRA-III synchrotron centre has been written and submitted.

01.07.2020.

Based on the inhouse and synchrotron characterisation of NiWO₄ and ZnWO₄ solid solutions, a paper entitled “X-ray absorption and Raman spectroscopy studies of tungstates solid solutions Zn_cNi_1-cWO₄ (c=0.0-1.0)” has been submitted to the journal of Low Temperature Physics.

Crystal computing code has been used to simulate polaron intercalation into the tungstate structure.

Two online workshops - organised by the DESY synchrotron in Hamburg - "X-ray Powder Diffraction - new opportunities for research and industry" (June 22-25) and "Perspectives and new opportunities for X-ray absorption spectroscopy" (June 29-30) have been attended.

01.04.2020.

A review of the scientific literature has been done. Practical training on the analytical methods available at the institute has been performed. NiWO₄, ZnWO₄ and CuMo_1-xW_xO₄ samples were synthesized and analyzed: their purity was confirmed by X-ray diffraction analysis and X-ray photoelectron spectroscopy. A research project for synchrotron measurements has been written and submitted. The preliminary acquaintance with Crystal computing code has begun.