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Local order in GdFe2 and LaNi5 hydrides and in new series of borohydrides

Applicant Cerny Radovan
Number 122123
Funding scheme Project funding (Div. I-III)
Research institution Laboratoire de Cristallographie Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Condensed Matter Physics
Start/End 01.10.2008 - 30.09.2010
Approved amount 108'360.00
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Keywords (5)

Powder Diffraction; Pair Distribution Function; Local Order; Metal Hydride; Hydrogen Storage

Lay Summary (English)

Lead
Lay summary
One objective of the project is the investigation the effect of hydrogen interaction with transition metal in the cubic Laves phase GdFe2, and in the battery material, hydride of LaNi5. GdFe2 shows several phase transitions under the interaction with hydrogen, including the transition crystalline - amorphous phase. In the case of the hydride of LaNi5 we want to show that this hydride traditionally described as interstitial can be in reality rationalized by local existence of hydrido-complexes [NiH4]4-. The Pair Distribution Function (PDF) analysis with the modeling of the PDF from well defined structural building blocks as available in existing programs or as will be implemented in our program FOX allows getting the information on the local structure regardless the state of the compound (crystalline or amorphous). The second objective is the synthesis of novel reversible metal hydrides with high hydrogen capacity (> 10 wt.%) with general formula MM’(BH4)4, where M and M’ is bivalent metal (Mg, Ca, bivalent d-metal) or M is monovalent metal (Li, Na, K, Cu) and M’ is trivalent metal (d-metal, Al) or M is tetravalent metal (Zr, Ti, V) and M’ is a vacancy. The idea of this series of compounds comes from the comparison of LiSc(BH4)4 and Mg(BH4)2. The crystal structures of both compounds were solved by us. In both compounds the coordination of the cations (Li, Sc, Mg) is the same (by four BH4 groups). The important amount of disorder but possibly local order involves again the use of PDF analysis. We want to understand the rules controlling the existence of ternary borohydrides by analyzing selected compounds from this series. It will allow later to start a broader project on a systematic search of reversible hydrogen absorbers in this system.The first part of the project is a continuation of the project No. 200021-107916 resulting in the conclusions about the conservation of the local configuration transition metal - deuterium in fully ordered and disordered phases. We want to extent now this conclusion also to amorphous state of the hydride.The second part is the application of the method for the analysis of average and local crystal structure to a completely new class of materials, potentially very interesting materials for hydrogen storage in mobile applications. In fact, contrary to what is commonly tried, the destabilization of light metals borohydrides, we propose to stabilize the d-metals borohydrides. The unfavorable thermodynamic properties of d-metals borohydrides will be modified by the partial substitution of d-metal by alkaline or alkaline earth metal with the aim to get the stoichiometry MM’(BH4)4.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Mitigation of Hydrogen Capacity Losses during Pressure Cycling of the Li3N–H System by the Addition of Nitrogen
Lamb Joshua, Chandra Dhanesh, Chien Wen-Ming, Phanon Delphine, Penin Nicolas, Černý Radovan, Yvon Klaus (2011), Mitigation of Hydrogen Capacity Losses during Pressure Cycling of the Li3N–H System by the Addition of Nitrogen, in The Journal of Physical Chemistry C, 115(29), 14386-14391.
Powder diffraction methods for studies of borohydride-based energy storage materials
Ravnsbaek DB, Filinchuk Y, Cerny R, Jensen TR (2010), Powder diffraction methods for studies of borohydride-based energy storage materials, in ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 225(12), 557-569.

Associated projects

Number Title Start Funding scheme
53847 Inorganic crystal structures from powder diffraction by a model building approach 01.10.1998 Project funding (Div. I-III)
131811 Bimetallic borohydrides: hydrogen storage and superionic conductivity. 01.10.2010 Project funding (Div. I-III)
107916 Local structure and lattice defects in metal hydrides and hydrogen absorbing intermetallic compounds 01.09.2005 Project funding (Div. I-III)
131811 Bimetallic borohydrides: hydrogen storage and superionic conductivity. 01.10.2010 Project funding (Div. I-III)

Abstract

Many disordered crystalline materials show chemical short range order and relaxation of neighboring atoms. Studying such materials is notoriously difficult. Recently, significant advances have been made using the atomic Pair Distribution Function (PDF) analysis of powder diffraction data coupled with the use of advanced X-ray and neutron sources and fast computers.Metal hydrides are examples of compounds where the atomic order, long and/or short range, are the mechanisms of controlling their properties like conductivity, optical state, magnetic interaction or hydrogen storage capacity. Interstitial hydrides, i.e. compounds formed from metals and intermetallic compounds by hydrogen absorption, have special properties. The lattice structure is that of a typical metal with atoms of hydrogen on the tetrahedral and octahedral interstitial sites; for this reason they are also called interstitial hydrides. Complex hydrides, on the other side, are formed either by hydrogen absorption by an intermetallic compound or directly from chemical elements. The interesting difference between the complex hydrides and interstitial ones is the transition of the metals to an ionic or covalent compound upon hydrogen absorption and a formation of metal-hydrogen complexes accompanied with a significant structural changes in complex hydrides. However, the boundary between interstitial and complex hydrides is not sharp, and a local existence of the metal-hydrogen complexes in the interstitial hydrides is discussed in the literature.In this project we want to continue the research started with the SNSF project No. 200021-107916 which focused on studies of local order and lattice defects in metal hydrides and hydrogen absorbing intermetallic compounds. The development of the powder diffraction methodology in the field of the application of PDF was and will be an important part of the project. The new methods were and will be implemented in the existing software (program FOX) developed in our laboratory as a SNSF project no. 21-53847.98. One objective of the continuation of the project is the investigation the effect of hydrogen interaction with transition metal in the cubic Laves phase GdFe2, and in the battery material, hydride of LaNi5. The study is motivated by our convincing results on the local structure of hydrides of other Laves phases. GdFe2 shows several phase transitions under the interaction with hydrogen, including the transition crystalline - amorphous phase. In the case of the hydride of LaNi5 we want to show that this hydride traditionally described as interstitial can be in reality rationalized by local existence of hydrido-complexes [NiH4]4-. The PDF analysis with the modeling of the PDF from well defined structural building blocks as available in existing programs like DISCUS or as will be implemented in our program FOX allows getting the information on the local structure regardless the state of the compound (crystalline or amorphous). The second objective is the synthesis of novel reversible metal hydrides with high hydrogen capacity (> 10 wt.%) with general formula MM’(BH4)4, where M and M’ is bivalent metal (Mg, Ca, bivalent d-metal) or M is monovalent metal (Li, Na, K, Cu) and M’ is trivalent metal (d-metal, Al) or M is tetravalent metal (Zr, Ti, V) and M’ is a vacancy. The idea of this series of compounds comes from the comparison of LiSc(BH4)4 and Mg(BH4)2. The crystal structures of both compounds were solved by us. In both compounds the coordination of the cations (Li, Sc, Mg) is the same (by four BH4 groups). The important amount of disorder but possibly local order involves again the use of PDF analysis. We want to understand the rules controlling the existence of these compounds by analyzing selected compounds from this series. It will allow later to start a broader project on a systematic search of reversible hydrogen absorbers in this system.The experimental work will be done at the powder diffraction installations at world leading synchrotron and neutron sources, such as Swiss-Norwegian Beamline at the ESRF in Grenoble, Swiss Light Source and SINQ at the PSI Villigen and LANSCE in Los Alamos. The international collaboration includes University J. Fourier and CEA in Grenoble, Laboratoire de Chimie Métallurgique des Terres Rares, CNRS, in Thiais and University of Nevada, Reno. The national collaboration includes Dpt. of Physical Chemistry, University of Geneva, Hydrogen & Energy EMPA, Dübendorf and Swiss-Norwegian Beamline at the ESRF in Grenoble.
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