From Materials to Crystallographic Analysis: An Neutrons/Materials/Powder Session

Conference: 2020: 70th ACA Annual Meeting
08/02/2020: 12:00 PM  - 3:00 PM 
Oral Session 


The Neutrons, Materials and Powder Diffraction SIGs are presenting a session that provides an opportunity to learn about materials ranging from correlated quantum materials to network structures, and new approaches to analyze crystallographic data.


Ternary alkali metal zinc antimonides and bismuthides: hydride synthesis and in-situ X-ray diffraction study

12:00 PM - 12:30 PM 
Materials discovery can be accelerated by the development of synthesis methods and in-situ characterization techniques allowing for the rapid "screening" of multicomponent systems. However, the sluggish kinetics of solid-state reactions entails the necessity of high temperatures and long annealing times, often leading to the stabilization of the thermodynamically stable products. Thus, new synthetic methods using unconventional reactive precursors must be developed to overcome limitations of traditional solid-state synthesis. Such methods will allow exploration of systems where starting materials have drastically different reactivity. We are interested in unconventional synthesis methods toward solid-state materials, using reactive, salt-like precursors. The chosen synthetic method utilizes alkali metal-hydride precursors and remedies the problem of insufficient mixing of the starting materials with ductile alkali metals, leading to faster kinetics and reduced annealing times. In addition, this route allows for targeted synthesis of specific compositions, and thus, fine tuning of physical properties. Such a synthetic approach could help bridge the gap between theoretical prediction and experimental synthesis of new materials, allowing for rapid exploration of potentially rich phase space in the ternary systems containing an alkali metal. Utilizing this synthesis method, new ternary alkali-metal zinc antimonides and bismuthides in the Na-Zn-Sb, Na-Zn-Bi, and K-Zn-Sb systems have been synthesized and characterized. These new compounds are hardly accessible via traditional solid-state route, because of the ductility and high reactivity of the alkali metal and side reactions resulting in inhomogeneous samples. The in-situ powder X-ray diffraction allowed to assess the thermal stability of the compounds and to further optimize synthesis of the phase pure samples. Additionally, in-situ powder X-ray diffraction helped to identify and subsequently synthesize high-temperature phases, which are hidden otherwise. 

View Abstract 426


Julia Zaikina, Department of Chemistry Iowa State University Ames, IA 

Additional Author(s)

Tori Cox, Department of Chemistry Iowa State University Ames, IA 
Volodymyr Gvozdetskyi, Department of Chemistry Iowa State University Ames, IA 

Structural chemistry of CuCN network solids with N-alkylethanolamine cation guests

12:30 PM - 1:00 PM 
We present structural data and chemical decomposition studies for seven CuCN network structures that include protonated alkylethanolamine derivatives as guest cations. Each 3D anionic polymeric structure is built from cyanide-bridged Cu atoms and is distinct from the others. All structures include cuprophilic pairs of Cu atoms as a building block, with Cu … Cu distances ranging from 2.46 to 2.73 Å. A typical unit is shown. Most Cu pairs have one or two µ3-CN groups bridging the pair of Cu atoms, but in one case there appears to be no such bridge. There appears to be some correlation between Cu … Cu distance and number of bridging pairs. Charge balance is provided by the protonated ethanolamine derivatives, but in two cases, the ethanolamine has apparently reacted with an aqueous CN- ion to form a cyclic oxazolidin cation. It is intriguing that thermogravimetric studies show a common theme of a mass decrease at 200-300oC that corresponds to the ethanolamine free base plus one HCN molecule to form CuCN. However, we have found no evidence for formation of the cyclic oxazolidine compound in the vapor phase in subsequent sublimation experiments. Conditions favoring formation of these cyclic compounds are under investigation. 

View Abstract 194


Peter Corfield, Chemistry, Fordham Univ Bronx, NY 

Additional Author(s)

Leena Rachid, Fordham University Bronx, NY 
Daniel Garcia, Fordham University Bronx, NY 
Faisal Elali, Fordham University Bronx, NY 
Gianni Contrera, Fordham University Bronx, NY 

Coffee Break

1:00 PM - 1:20 PM 

Crystallographic Description of Ordered Toroidal Moments

1:20 PM - 1:45 PM 
The symmetry of a quantum material system enables us to understand and predict the system's properties under different thermodynamic conditions. This is particularly true in ferroic systems, which are classified by the broken symmetry across their temperature-dependent phase transitions. For example, above the transition temperature of a ferromagnet under no applied field, the magnetic moments are randomly oriented in a paramagnetic state. Below the transition temperature, the moments align along a crystallographic direction, breaking time-inversion symmetry. In addition to the three well-studied classes of ferroics (ferromagnets, ferroelectrics, and ferroelastic) we are studying materials expected to exhibit ordering according to a fourth category, known as ferrotoroidics. As a ferrotoroidic material is cooled below its ordering temperature into a magnetically ordered state, the toroidal moments align along a crystallographic direction, breaking space-time inversion symmetry. Candidate ferrotoroidic materials are proposed based upon their magnetic point group symmetry and magnetoelectric properties [1]. The most well-studied candidate material is LiCoPO[sub]4[/sub]. Notably, Zimmerman and Fiebig [i]et al.[/i] performed second harmonic generation experiments on LiCoPO[sub]4[/sub] under magnetic and electric fields and observed a hysteretic response characteristic of ferroics [2]. There are several structural analogs to LiCoPO[sub]4[/sub], including LiFePO[sub]4[/sub] which exhibits the same magnetic structure as LiCoPO[sub]4[/sub] ([i]Pnma'[/i]), as well as LiMnPO[sub]4[/sub] whose magnetic structure would not permit ferrotoroidal order ([i]Pn'm'a'[/i]). Two years ago at this conference, I presented results of neutron diffraction studies on solid solutions between these end members LiMn[sub][i]x[/i][/sub]Co[sub]1-[i]x[/i][/sub]PO[sub]4[/sub] and LiMn[sub][i]x[/i][/sub]Fe[sub]1-[i]x[/i][/sub]PO[sub]4[/sub]. For all the studied members, they exhibited the same magnetic space group symmetry as LiCoPO[sub]4[/sub], which is evidence that this series of materials can be considered tunable ferrotoroidic candidates. In the following year I developed this idea further, extending the model for ordered toroidal moments proposed by Ederer and Spaldin [3] to these series as well as other candidate materials. The purpose of this presentation is discuss how to not only model a ferrotoroidic state, but also a paratoroidic, antiferrotoroidic, and nonferrotoridic system according to crystallographic conventions. [1] Gnewuch, S.; Rodriguez, E.E. [i]J. Solid State Chem.[/i] [b]2019[/b], [i]271[/i], 175 - 190. [2] Zimmerman, A. [i]et al. Nature Comm.[/i] [b]2014[/b], [i]5[/i], 4796. [3] Ederer, C.; Spaldin, N. A. [i]Phys. Rev. B[/i] [b]2007[/b], [i]76[/i], 214404. Acknowledgements: The authors gratefully acknowledge funding from the U.S. DOE Office of Science (Grant#: DE-SC0016434). 

View Abstract 162


Stephanie Gnewuch, University of Maryland, College Park Maryland, MD 

Additional Author

Efrain Rodriguez, University of Maryland College Park, MD 

Magnetic and Structural Properties of Thiophosphates Li2MP2S6 where M = Fe and Co

1:45 PM - 2:10 PM 
Ferrotoroidics are a member of the ferroic materials family. Similar to the well-known types of ferroic orders (ferromagnetic, ferroelectric, and ferroelastic), ferrotoroidics undergo a spontaneous, physical change below a critical temperature. In this case, the change is a spontaneous alignment of toroidal moments. A toroidal moment is defined as the local moment that arises from a local vortex of magnetic moments [1]. Due to the potential applications in data storage and memory, the purpose of this research is to further support and expand the current understanding of ferrotoroidic materials. An example candidate for ferrotoroidic materials are lithium transition metal thiophosphates of the formula Li2MP2S6, where M = Fe, Co. The thiophosphates were chosen because of their structural relations to LiCoPO4, which is arguably the most well studied ferrotoroidic [2]. Figure 1 depicts the layered honeycomb crystal structure of Li2FeP2S6 found by Takada et al. using x-ray diffraction [3]. To the best of our knowledge, no magnetic properties of this material have been studied. In addition, neither the structural nor magnetic properties have been reported for the cobalt analog. Phase pure powders of both Li2FeP2S6 and Li2CoP2S6 have been synthesized via a solid-state method. Layered, black, metallic-like crystals have been synthesized, growing up to 6 mm long. The crystal structure of Li2FeP2S6 reported by Takada et al. was confirmed using x-ray diffraction. The crystal structure of Li2CoP2S6, which has not been published, was also determined using the single crystals that were grown. SQUID magnetometry demonstrated an antiferromagnetic to paramagnetic transition at 25 K for the iron sample, but demonstrated paramagnetic behavior for the cobalt sample down to 2 K. The magnetometry results suggest an antiferromagnetic ordering of the magnetic moments in the iron sample, while the cobalt sample suggests no sign of magnetic ordering. In order to further confirm or refute the magnetometry data, time-of-flight neutron powder diffraction was used to analyze each of these samples. The resultant neutron powder diffraction for the cobalt patterns were identical both above and below the transition temperature, suggesting that there is no magnetic ordering. This same result was observed for the iron sample. The purpose of this presentation is twofold: a) to discuss the novel structural and magnetic properties of the lithium transition metal thiophosphates, and b) to relate this data back to the overarching goal, ferrotoroidicity. References: 1) Schmid, H. Ferroelectrics 2001, 252, 41-50. 2) Zimmermann, A. S.; Meier, D.; Fiebig, M. Nature Commun. 2014, 5, 4796. 3) Takada, K.; Tabuchi, M. Solid State Ion. 2003, 159, 257-263. Acknowledgements: This work was funded by the U.S. DOE Office of Science (Grant#: DE-SC0016434). The authors would also like to acknowledge Oak Ridge National Laboratory for the use of their neutron powder diffractometer. 

View Abstract 168


Timothy Diethrich, University of Maryland, College Park Rockville, MD 

Additional Author

Efrain Rodriguez, University of Maryland College Park, MD 

Bayesian refinement of full profile diffraction patterns for uncertainty quantification

2:10 PM - 2:35 PM 
Advancements in x-ray and neutron characterization instruments provide the ability to examine the structures of newly developed materials. Full profile diffraction patterns collected from these instruments can be analyzed through Rietveld refinements using least-squares fitting routines to obtain sample, structural, lattice, and instrumental parameters. An alternative statistical framework using a Bayesian analysis method can also be applied to full profile fitting in order to quantify the uncertainty in the model parameters [1]. In Bayesian inference, parameters are taken to be random variables having associated posterior distributions. This representation provides descriptive insight to the uncertainties in the parameters and the model fits. In this work, Rietveld refinements are initially performed with GSAS-II [2] on the metastable perovskite material system of (Ba[sub]1-x[/sub]Sn[sub]x[/sub])(Zr[sub]0.5[/sub]Ti[sub]0.5[/sub])O[sub]3[/sub] (BSZT) [3]. The Bayesian refinement method is then employed to enrich the model information, specifically to provide higher fidelity uncertainty quantification on the atomic occupancies and positions. The effects of refining instrumental parameters via the Bayesian method are also investigated. [1] C. M. Fancher, Z. Han, I. Levin, K. Page, B. J. Reich, R. C. Smith, A. G. Wilson, and J. L. Jones, "Use of Bayesian Inference in Crystallographic Structure Refinement via Full Diffraction Profile Analysis," Scientific Reports, Vol. 6, No. 31625 (2016). [2] B. H. Toby and R. B. Von Dreele, "GSAS-II: the genesis of a modern open-source all purpose crystallography software package," Journal of Applied Crystallography, Vol. 46, No. 2, pp. 544-549 (2013). doi:10.1107/S0021889813003531 [3] S. O'Donnell, C. C. Chung, A. Carbone, R. Broughton, J. L. Jones, and P. A. Maggard, "Pushing the Limits of Metastability in Semiconducting Perovskite Oxides for Visible Light-Driven Water Oxidation," Chemistry of Materials, Vol. 32, No. 7, pp. 3054-3064 (2020). 

View Abstract 203


Rachel Broughton, North Carolina State University Raleigh, NC 

Additional Author(s)

Shaun O'Donnell, North Carolina State University Raleigh, NC 
Eric Gabilondo, North Carolina State University Raleigh, NC 
Ching-Chang Chung, North Carolina State University Raleigh, NC 
Paul Maggard, North Carolina State University Raleigh, NC 
Alyson Wilson, North Carolina State University Raleigh, NC 
Brian Reich, North Carolina State University Raleigh, NC 
Ralph Smith, North Carolina State University Raleigh, NC 
Jacob Jones, North Carolina State University Raleigh, NC 

Measurement of partial atomic charges by least-squares refinement of variable electron density crystallographic models.

2:35 PM - 3:00 PM 
Of interest in understanding electronic structure, bulk physical properties, enthalpies of phase changes, dipole moments, and numerous other properties of molecules, is the determination of realistic partial atomic charges on atoms. Atoms may take on partial positive or negative charges due to polar covalent bonds, coordinate covalent bonds, or due to formal charges imposed by Lewis structure constraints. Traditional crystallographic refinement treats each atom as a neutral, spherical atom however. We present a ongoing developments of a mode of crystallographic model refinement that permits refinement of electron density at individual atoms in order to arrive at partial atomic charges of atoms in a crystallographic model. Comparison to calculated partial charges (CHELPG, NBO, Mulliken) from quantum calculations (DFT, MP2) in both the gas phase and crystalline state will be presented. 

View Abstract 353


Michael Zdilla, Chemistry, Temple Univ Philadelphia, PA 

Additional Author(s)

Taylor Keller, Temple University Philadelphia, PA 
Prabhat Prakash, Temple University Philadelphia, PA 
Alex Byrne, Temple University Philadelphia, PA