scholarly journals On the crystal chemistry of inorganic nitrides: crystal-chemical parameters, bonding behavior, and opportunities in the exploration of their compositional space

2021 ◽  
Author(s):  
Olivier C. Gagné
Keyword(s):  
Crystal Chemistry ◽  
Functional Properties ◽  
Crystal Chemical ◽  
Chemical Parameters ◽  
High Return ◽  
Compositional Space

Navigating high-return chemical spaces in inorganic nitrides via identification of coordination units bearing functional properties.

On the Crystal Chemistry of Inorganic Nitrides: Crystal-Chemical Parameters and Opportunities in the Exploration of Their Compositional Space

2020 ◽  
Author(s):  
Olivier Charles Gagné
Keyword(s):  
Functional Properties ◽  
A Priori ◽  
Lone Pair ◽  
Length Variation ◽  
Electronic Effects ◽  
Statistical Knowledge ◽  
Redox Active ◽  
Multiply Bonded ◽  
Jahn Teller ◽  
Compositional Space

The scarcity of nitrogen in Earth’s crust, combined with challenging synthesis, have made inorganic nitrides a relatively-unexplored class of compounds compared to their naturally-abundant oxide counterparts. To facilitate exploration of their compositional space via <i>a priori</i> modeling, and to help <i>a posteriori</i> structure verification not limited to inferring the oxidation state of redox-active cations, we derive a suite of bond-valence parameters and Lewis-acid strength values for 76 cations observed bonding to N<sup>3-</sup>, and further outline a baseline statistical knowledge of bond lengths for these compounds. We examine structural and electronic effects responsible for the functional properties and anomalous bonding behavior of inorganic nitrides, and identify promising venues for exploring uncharted compositional spaces beyond the reach of high-throughput computational methods. We find that many mechanisms of bond-length variation ubiquitous to oxide and oxysalt compounds (e.g., lone-pair stereoactivity, the Jahn-Teller and pseudo Jahn-Teller effects) are similarly pervasive in inorganic nitrides, and are occasionally observed to result in greater distortion magnitude than their oxide counterparts. We identify inorganic nitrides with multiply-bonded metal ions as a promising venue in heterogeneous catalysis, e.g. in the development of a post-Haber-Bosch process proceeding at milder reaction conditions, thus representing further opportunity in the thriving exploration of the functional properties of this emerging class of materials.<br>

scholarly journals Geometrical parameterization of the crystal chemistry ofP63/mapatite. II. Precision, accuracy and numerical stability of the crystal-chemical Rietveld refinement

2006 ◽  
Vol 39 (3) ◽  
pp. 369-375 ◽  
Author(s):  
Patrick H. J. Mercier ◽  
Yvon Le Page ◽  
Pamela S. Whitfield ◽  
Lyndon D. Mitchell
Keyword(s):  
Least Squares ◽  
Rietveld Refinement ◽  
Numerical Stability ◽  
Structural Parameters ◽  
Structure Refinement ◽  
Standard Uncertainty ◽  
Crystal Chemical ◽  
Chemical Parameters ◽  
Cell Parameters ◽  
Order Of Magnitude

A script developed for crystal-chemical Rietveld refinement ofP63/mapatite withTOPASis implemented in parallel with standard structure refinement. Least-squares standard uncertainty (s.u.) values for directly extracted crystal-chemical parameters are nearly an order of magnitude lower than those obtained indirectly by analysis of atom coordinates derived by standard Rietveld refinement. This amazing finding originates partly in the reduction of the number of refinement parameters from 21 to 17 and partly in the fact that cell data now derive from crystal-chemical parameters instead ofvice versa. Great precision and accuracy otherwise funneled into unit-cell parameters is then more distributed among mostly crystal-chemical distance parameters. The least-squares s.u. values are supported by analysis of numerous refinements of the same experimental data with added artificial intensity noise. Structural parameters from single-crystal results agree better with those extracted by crystal-chemical refinement. On the basis of singular value decomposition analyses performed using the programSVDdiagnostic[Mercieret al.(2006).J. Appl. Cryst.39, 458–465], crystal-chemical and standard Rietveld refinements are shown to have similar numerical stability. Crystal-chemical parameters extracted by direct Rietveld refinement, therefore, are more precise than, more accurate than and numerically as reliable as those derived from analysis of regular crystallographic refinement of the same data.

scholarly journals Geometrical parameterization of the crystal chemistry of P63/m apatites: comparison with experimental data and ab initio results

2005 ◽  
Vol 61 (6) ◽  
pp. 635-655 ◽  
Author(s):  
Patrick H. J. Mercier ◽  
Yvon Le Page ◽  
Pamela S. Whitfield ◽  
Lyndon D. Mitchell ◽  
Isobel J. Davidson ◽  
...  
Keyword(s):  
Single Crystal ◽  
Ab Initio ◽  
Minimum Energy ◽  
Structure Type ◽  
Chemical Model ◽  
Crystal Chemical ◽  
Chemical Parameters ◽  
Rietveld Refinements ◽  
Cell Parameters ◽  
Cell Data

Experimental structure refinements and ab initio simulation results for 18 published, fully ordered P63/m (A^{\rm I}_4)(A^{\rm II}_6)(BO4)6 X 2 apatite end-member compositions have been analyzed in terms of a geometric crystal-chemical model that allows the prediction of unit-cell parameters (a and c) and all atom coordinates. To an accuracy of ± 0.025 Å, the magnitude of c was reproduced from crystal-chemical parameters characterizing chains of …–A II–O3–B–O3–A II–... atoms, whereas that of a was determined from those describing (A IO6)–(BO4) polyhedral arrangements. The c/a ratio could be predicted to ±0.2% using multi-variable functions based on geometric crystal-chemical model predictions, but could not be ascribed to the adjustment of a single crystal-chemical parameter. The correlations observed between algebraically independent crystal-chemical parameters representing the main observed polyhedral distortions reveal them as the minimum-energy solution to accommodate misfit components within this flexible structure type. For materials with given composition, good agreement (within ± 0.5–2.0%) of ab initio crystal-chemical parameters was observed with only those from single-crystal refinements with R ≤ 4.0%. Agreement with single-crystal work with R > 4.0% was not as good, while the scatter with those from Rietveld refinements was considerable. Accordingly, ab initio cell data, atomic coordinates and crystal-chemical parameters were reported here for the following compositions awaiting experimental work: (Zn,Hg)10(PO4)6(Cl,F)2, (Ca,Cd)10(VO4)6Cl2 and (Ca,Pb,Cd)10(CrO4)6Cl2.

Relationship Between Thermal Expansion and Crystal Chemical Parameters in Diborides

1986 ◽  
Vol 30 ◽  
pp. 503-510
Author(s):  
H.A. McKinstry ◽  
Lai Daik Chai ◽  
R.V. Sara ◽  
K.E. Spear
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Zirconium Phosphate ◽  
Hexagonal Structure ◽  
Crystal Chemical ◽  
X Ray Diffraction ◽  
Chemical Parameters ◽  
X Ray ◽  
Sodium Zirconium ◽  
Sodium Zirconium Phosphate

Thermal expansion is an interesting, ubiquitous and neglected property of materials. Recently, Lenain et al. (1985) and Limaye (1986) have been investigating anisotropy in the low-expansion structures of the sodium zirconium phosphate family. In the hexagonal structure one axis expands while another contracts. In going from the calcium to the strontium analog the anisotropy actually changes sign. A change in anisotropy between CrB2 and TiB2 had been observed by R.V. Sara (1960). The results in Fig. 1 obtained by high temperature x-ray diffraction measurements indicate that for TiB2 the thermal expansion of the c-axis is greater than the expansion of the a-axis, whereas for CrB2 the reverse is true.

Crystal chemistry of ettringite

1962 ◽  
Vol 33 (256) ◽  
pp. 59-64 ◽  
Author(s):  
Duncan McConnell ◽  
Joseph Murdoch
Keyword(s):  
Crystal Chemistry ◽  
Simple Form ◽  
Unit Cell ◽  
Crystal Chemical ◽  
Aluminium Sulphate ◽  
Hexagonal Unit Cell ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Anionic Groups ◽  
Oxygen Atoms

Summary Crystal-chemical calculations are based on three chemically analysed samples of ettringite and their respective unit-cell dimensions and specific gravities. The large hexagonal unit cell is deduced to contain 384 oxygen atoms, 64 cations with co-ordination number 6 or more, and 48 cations with co-ordination number 4 or less. Some substitution of cations with co-ordination number 3 apparently takes place, and any excess above 192 H2O takes place in the form of substitution of (H4O4) for XO4 anionic groups. The isomorphism is extremely complex but can be generalized in simple form as 16[A4(XO4)3(H2O)12], where A represents atoms with six-fold co-ordination (Ca, Na, Al) and X represents atoms with four-fold coordination (S, Si, H4, and possibly some of the Al). It is implied that an isostructural series of silicon-containing calcium aluminium sulphate hydrates might exist, the extreme compositions of which are: 6CaO.Al2O3.3SO3.3SiO2.24H2O and 6CaO.Al2O3.3SO3.30H2O.

A review of crystal chemistry of natural silicates of alkaline elements in the light of new structural data

2014 ◽  
Vol 78 (2) ◽  
pp. 253-265 ◽  
Author(s):  
N. V. Zubkova ◽  
I. V. Pekov ◽  
D. Yu. Pushcharovsky
Keyword(s):  
Crystal Structures ◽  
Crystal Chemistry ◽  
Structural Data ◽  
Crystal Chemical ◽  
Chemical Feature ◽  
New Members ◽  
Silanol Groups ◽  
Crystal Chemical Feature

AbstractA review is presented here of the crystal chemistry of natural silicates of alkaline elements, mainly Na, with a focus on reporting recent data on the structural mineralogy of the new members of this chemical family and their crystal structures. The majority of the natural hydrous silicates of alkaline elements studied are characterized by a specific crystal-chemical feature − the presence of silanol groups Si−OH. The discovery of the two new minerals, chesnokovite and yegorovite, means that all the main topological types of the [SixOy] complexes are represented in the crystal structures for this family.

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