Ca(NiO2)2

High-Entropy Materials HEA Traditional Materials TRA

MP-ID: mp-1047720 · Space group: Cmcm (#63)

Materials Project API

Basic Information

Formula

Ca(NiO2)2

MP-ID

mp-1047720

Elements

Sites

Density

5.0817

g/cm³

Volume

144.73

Å³

Cell a

5.1354

Cell b

5.1354

Cell c

9.6198

α Angle

90.00

β Angle

90.00

γ Angle

145.22

Space Group

Cmcm

Point Group

mmm

Crystal System

Orthorhombic

Bravais Lattice

Stability

Packing Fraction

X-ray Diffraction

Diffraction Pattern

Target / Radiation

X-axis: 2θ (°); Y-axis: relative intensity; Cu Kα ; λ=1.5418 Å

Diffraction Peaks (Top 24)

2θ	d (Å)	I	hkl
18.10	4.9006	2.7	(1,-1,0)
18.45	4.8099	26.8	(0,0,2)
20.34	4.3667	5.9	(1,-1,1)
25.96	3.4327	6.8	(1,-1,2)
30.51	2.9297	17.4	(1,0,0)
31.93	2.8026	30.1	(1,0,1)
33.39	2.6832	100.0	(1,-1,3)
35.89	2.5021	25.4	(1,0,2)
36.68	2.4503	23.9	(2,-2,0)
37.39	2.4050	1.3	(0,0,4)
40.31	2.2373	37.1	(2,-1,0)
41.35	2.1833	1.2	(2,-2,2)
41.44	2.1791	49.5	(2,-1,1)
41.76	2.1629	6.2	(1,0,3)
41.84	2.1590	11.2	(1,-1,4)
44.67	2.0286	53.5	(2,-1,2)
46.65	1.9470	1.1	(2,-2,3)
49.00	1.8589	7.2	(1,0,4)
49.69	1.8348	4.2	(2,-1,3)
50.99	1.7909	8.6	(1,-1,5)
56.15	1.6381	2.2	(2,-1,4)
56.52	1.6283	6.9	(3,-2,1)
57.29	1.6082	26.4	(1,0,5)
57.48	1.6033	13.0	(0,0,6)

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Energy Properties

Formation Energy/atom

-1.62120

eV/atom

Energy/atom

-6.38659

eV/atom

Energy above Hull

0.0409

eV/atom

Uncorrected Energy

-5.2680

eV/atom

Volume/atom

10.34

Å³

c/a Ratio

1.8732

Electronic Properties

Metallic

Metal

Band Gap

Direct Gap

CBM

N/A

Magnetic Properties

Magnetic

Yes

Total Mag. Moment

3.9984

μB

Mag. Ordering

FiM

Mag. Sites

Magnetization/Volume

0.027630

μB/Å³

Elastic Properties

Elastic data not available

Feature Analysis

Composition Overview

Element Composition (atomic fraction)

Composition Info

Major / Matrix Element

O · 0.571

Element Family

Metalloid-Nonmetal

Solute Fraction

0.429

Interstitial Fraction

0.000

High-Entropy Alloy Features

Composite Radar (normalized)

Element-Class Share

Mix Entropy ΔS/R

0.9557

HEA criterion (>1.0 = high entropy)

Mix Entropy ΔS

7.9457

J/mol·K

Ω Parameter

1.6573

Ω > 1.1 favors solid solution

Atomic Size Mismatch δr

50.254%

δr < 6.6% favors single-phase solid solution

Electronegativity Diff Δχ

0.9497

smaller = more stable mixing

VEC

5.429

valence electron concentration, affects phase stability

Mix Enthalpy ΔH_mix

-3.281

kJ/mol; negative = exothermic mixing

Entropy Norm

0.8699

SS Former

Phase Tendency

Traditional Material Features

ROM Blended-Feature Radar

Rating & Classification

Tier

Score

0.535

Family

O-rich Multi-Component

Matrix Element

O · 0.571

Related Tasks

Related computation task IDs (3)

aaachpxx aaadvdcb aaadxhua

Citation & References

Materials Project Page

https://materialsproject.org/materials/mp-1047720

Reference Citation

The crystal structure and related material properties of Ca(NiO2)2 were obtained from the Materials Project database (MP-ID: mp-1047720, database version v2026.04.13).

Literature Citation

Horton, M.K., Huck, P., Yang, R.X. et al. Accelerated data-driven materials science with the Materials Project. Nat. Mater. 24, 1522–1532 (2025). https://doi.org/10.1038/s41563-025-02272-0

3D Crystal Structure Rendering

Loading 3D structure…

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Raw CIF Data

# generated using pymatgen
data_Ca(NiO2)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.13541167
_cell_length_b   5.13541167
_cell_length_c   9.61980000
_cell_angle_alpha   90.00000000
_cell_angle_beta   90.00000000
_cell_angle_gamma   145.21530626
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Ca(NiO2)2
_chemical_formula_sum   'Ca2 Ni4 O8'
_cell_volume   144.73307509
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Ca  Ca0  1  0.60608900  0.39391100  0.75000000  1.0
  Ca  Ca1  1  0.39391100  0.60608900  0.25000000  1.0
  Ni  Ni2  1  0.13825400  0.86174600  0.06817200  1.0
  Ni  Ni3  1  0.86174600  0.13825400  0.93182800  1.0
  Ni  Ni4  1  0.13825400  0.86174600  0.43182800  1.0
  Ni  Ni5  1  0.86174600  0.13825400  0.56817200  1.0
  O  O6  1  0.76885800  0.23114200  0.39380500  1.0
  O  O7  1  0.23114200  0.76885800  0.60619500  1.0
  O  O8  1  0.23114200  0.76885800  0.89380500  1.0
  O  O9  1  0.76885800  0.23114200  0.10619500  1.0
  O  O10  1  0.06205500  0.93794500  0.25000000  1.0
  O  O11  1  0.93794500  0.06205500  0.75000000  1.0
  O  O12  1  0.50000000  0.50000000  0.00000000  1.0
  O  O13  1  0.50000000  0.50000000  0.50000000  1.0

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