Nickel forms a series of mixed oxide compounds which are commonly called nickelates. A nickelate is an anion containing nickel or a salt containing a nickelate anion, or a double compound containing nickel bound to oxygen and other elements. Nickel can be in different or even mixed oxidation states, ranging from +1, +2, +3 to +4. The anions can contain a single nickel ion, or multiple to form a cluster ion. The solid mixed oxide compounds are often ceramics, but can also be metallic. They have a variety of electrical and magnetic properties. Rare-earth elements form a range of perovskite nickelates, in which the properties vary systematically as the rare-earth element changes. Fine tuning of properties is achievable with mixtures of elements, applying stress or pressure, or varying the physical form.
Inorganic chemists call many compounds that contain nickel centred anions "nickelates". These include the chloronickelates, fluoronickelates, tetrabromonickelates, tetraiodonickelates, cyanonickelates, nitronickelates and other nickel-organic acid complexes such as oxalatonickelates.
Alkali nickelates The lithium nickelates are of interest to researchers as cathodes in lithium cells, as these substance can hold a variable amount of lithium, with the nickel varying in oxidation state.
Rare-earth nickelates Rare-earth nickelates were first made by Demazeau et al. in 1971, by heating a mixture of oxides under high pressure oxygen, or potassium perchlorate. For two decades after that these nickelates received very little attention. Many rare-earth nickelates have the Ruddlesden–Popper phase structure.
Rare-earth nickelates with nickel in a +1 oxidation state have an electronic configuration to same as for cuprates and so are of interest to high-temperature superconductor researchers. Other rare-earth nickelates can function as fuel cell catalysts. The ability to switch between an insulating and a conducting state in some of these materials is of interest in the development of new transistors, that have higher on to off current ratios.
List of oxides formulanameother namesstructureRemarksreferencesLiNiO2lithium nickelaterhombohedral a = 2.88 Å, c = 14.2 Å, density = 4.78 / 4.81Li2NiO3monoclinic C2/m a = 4.898 Å, b = 8.449 Å, c = 4.9692 Å, β = 109.02°, V = 194.60 Å3Nickel in +4 stateNaNiO2sodium nickelatemonoclinic a = 5.33 Å, b = 2.86 Å, c = 5.59 Å, β = 110°30′, Z = 2, density = 4.74; over 220 °C: rhombohedral a = 2.96 Å, b = 15.77 ÅCarbon dissolved in the molten salt can precipitate diamond. KNiO2potassium nickelateSrTiNiO3strontium titanate nickelateSTNYNiO3yttrium nickelatemonoclinic P21/n; orthorhombic a = 5.516 Å, b = 7.419 Å, c = 5.178 Å, V = 211.9 Å3, Z = 4, density = 6.13insulator changes to metal under pressureY2BaNiO5chain nickelateOrthorhombic Immm, a = 3.7589, b = 5.7604, c = 11.33112H-AgNiO2hexagonal P63/mmc, a = 2.93653 Å, b = 2.93653 Å, c = 12.2369 Å, V = 91.384 Å3, Z = 2, density = 7.216 g/cm3Ni in +3 state3R-AgNiO2trigonal R2/m, a = 2.9390 Å, c = 18.3700 ÅNi in +3 stateAg2NiO2silveroxonickelatetrigonal R2/m, a = 2.926 Å, c = 24.0888 Ålustrous black solid, stable in air; Ni3+ and subvalent Ag2+Ag3Ni2O4hexagonal P63/mmc, a = 2.9331 Å, b = 2.9331 Å, c = 28.31 Å, V = 210.9 Å3, Z = 2, density = 7.951 g/cm3electric conductorBaNiO2orthorhombic a = 5.73 Å, b = 9.2 Å, c = 4.73 Å, V = 249 Å3, Z = 4blackBaNiO3hexagonal a = 5.580 Å, c = 4.832 Å, V = 130.4 Å3, Z = 2black powder dec 730 °C N-type semiconductor; decompose in acidBa2Ni2O5hexagonal a = 5.72, c = 4.30, density = 6.4black needles melt 1200 °C LaNiO2lanthanum nickelitea = 3.959, c = 3.375Ni in +1 stateLaNiO3lanthanum nickelate a = 5.4827 Å, b = 5.4827 Å, c = 3.2726 Å, γ = 120°, V = 345.5, Z = 6, density = 7.08metallic, no insulating transition polar metalLa2NiO4LNtetragonal a = 3.86 Å, b = 3.86 Å, c = 12.67 Å, V = 188.8 Å3, Z = 2, density = 7.05La3Ni2O6tetragonal a = 3.968 Å, c = 19.32 ÅLa3Ni2O7a = 5.3961 Å, b = 5.4498 Å, c = 20.522 Å, V = 603.5, Z = 4, density = 7.1superconductor under pressure Tc=80KLa4Ni3O8antiferromagnetic below 105 K, mixed valence I and IILa4Ni3O10La2−xSrxNiO4LSNa varies from 3.86 to 3.81 as x changes from 0 to 0.5, then ≈ 3.81; c ≈ 12.7 for x ≤ 0.8, the it falls to 12.4 at x = 1.2polarization-specific metalCeNiO3cerium nickelatedecomposes 1984 °CPrNiO2PrNiO3 perovskitemetallic insulator transition=130KPr4Ni3O8Pr2BaNiO5chain nickelateOrthorhombicLa2PrNi2O7orthorhombicLa2PrNi2O7tetragonalSuperconductor under pressure Tc = 82.5 KNdNiO3neodymium nickelate perovskite orthorhombic Pbnm, a = 5.38712 Å, b = 5.38267 Å, c = 7.60940 Åmetallic insulator transition=200K NdNiO2orthorhombic a = 5.402 Å, b = 7.608 Å, c = 5.377 Å, V = 221.0 Å3, density = 7.54Nd4Ni3O8orthorhombic a = 3.9171 Å, b = 3.9171 Å, c = 25.307 Å, V = 388.3 Å3, Z = 2, density = 7.54Nd2NiO4Cmca a = 5.383 Å, b = 12.342 Å, c = 5.445 Å, V = 361.7 Å3, density = 7.55Nd2BaNiO5chain nickelateOrthorhombic Immm, a = 2.8268 Å, b = 5.9272 Å, c = 11.651 ÅSmNiO3samarium nickelateSNO perovskite Pnma, a = 5.431 Å, b = 7.568 Å, c = 5.336 Å, V = 219.3 Å, Z = 4, density = 7.79metallic insulator transition=400KSm1.5Sr0.5NiO4SSNOorthorhombic Bmabgiant dielectric constant 100,000EuNiO3europium nickelate perovskite orthorhombic a = 5.466 Å, b = 7.542 Å, c = 5.293 Å, V = 218.2 Å3, Z = 4, density = 7.87metallic insulator transition=460KGdNiO3gadolinium nickelate perovskite orthorhombic a = 0.5492 Å, b = 0.7506 Å, c = 0.5258 Å, V = 216.8 Å3, Z = 4, density = 8.09metallic insulator transition=510.9KGd2NiO4digadolinium nickelateOrthorhombic a = 3.851 Å, b = 3.851 Å, c = 6.8817 Å, V = 187.5 Å3, Z = 2, density = 7.75BaGd2NiO5barium digadolinium nickelatechain nickellate?orthorhombiclow thermal conductanceTb2BaNiO5chain nickelateOrthorhombicDyNiO3dysprosium nickelate perovskite orthorhombic a = 0.55 Å, b = 0.7445 Å, c = 0.5212 Å V=213.4 Z=4 density=8.38metallic insulator transition=564.1KDy2BaNiO5chain nickelateOrthorhombicHoNiO3holmium nickelate perovskite orthorhombic a = 3.96 Å, b = 3.96 Å, c = 5.04 Å, V = 212 Å3 Z = 4, density=8.51 metallic insulator transition=560KHo2BaNiO5chain nickelateOrthorhombic Immm, a = 3.764 Å, b = 5.761 Å, c=11.336 ÅErNiO3erbium nickelate perovskite orthorhombic a = 5.514 Å, b =7.381 Å, c = 5.16 V=201 Z=4 density=8.67metallic insulator transition=580KEr2BaNiO5chain nickelateOrthorhombic Immm a = 3.7541 Å, b = 5.7442 Å c=11.3019 Å V=243.71 Å3 Z=2TmNiO3thulium nickelateorthorhombic a = 5.495 Å, b = 7.375 Å, c = 5.149 Å V = 208.7 Z = 4 density = 8.77Tm2BaNiO5thulium barium nickelateOrthorhombic low temperature Pnma a = 12.2003 Å b = 5.65845 Å c = 6.9745 Å Z = 4; high T: Immm a = 3.75128 b = 5.7214 c = 11.2456Pnma form is brown Immm form is dark greenYbNiO3ytterbium nickelateOrthorhombic a = 5.496 Å, b = 7.353 Å, c = 5.131 Å Z=4 V=207.4 Å3 density=8.96Yb2BaNiO5ytterbium barium nickelateOrthorhombic Pnma a = 5.6423 Å, b = 6.9545 Å, c = 12.1583 Å V=477.1 Z=4 density=8.66Pnma form is brown LuNiO3lutetium nickelate perovskite a = 5.499 Å, b = 7.356 Å, c = 5.117 Å, V = 207 Å3, Z = 4, density = 9.04metallic insulator transition=600KLu2BaNiO5Orthorhombic PnmaTlNiO3thallium nickelate(III)perovskite a = 5.2549 Å, b = 5.3677 Å, c = 7.5620 Å, V = 213.3 Å3PbNiO3 BiNiO3bismuth nickelate(III)perovskite triclinic a = 5.3852, b = 5.6498, c = 7.7078 Å, α = 91.9529°, β = 89.8097°, γ = 91.5411, V = 234.29 Å3Ni in +2 state, Bi in +3 and +5; stable 5–420K, antiferromagnetic
See also Nickel manganese oxides for what are considered nickel manganates
References