HfO2-based refractory compounds and solid solutions: 2. Kinetics and mechanism of compound formation in the systems HfO2M2O3 (MO)

doi:10.1016/0272-8842(85)90002-1

Ceramics International

Volume 11, Issue 3, July–September 1985, Pages 80-90

https://doi.org/10.1016/0272-8842(85)90002-1 Get rights and content

Abstract

In a previous communication¹ we considered the papers published in the USSR on studies of phase diagrams for the systems hafnia-alkali-earth oxides and hafnia — rare-earth oxides. The purpose of many investigations was the preparation of new refractory compounds and solid solutions which could create the basis of high-refractory materials. In addition to the great analogy between binary systems with hafnia and zirconia, our interest in hafnium-containing compounds was promoted by their higher melting temperatures compared with those of zirconia-based compounds and by several peculiar physico-chemical properties characteristic of hafnia-based compounds and solid solutions. It has been shown¹ in the HfO₂ single bond MO systems, strontium forms the greatest number of compounds: SrHfO₃, Sr₂HfO₄, Sr₃Hf₂O₇ and Sr₄Hf₃O₁₀; calcium forms two compounds: CaHfO₃ and CaHf₄O₉; barium and magnesium each produce one compound: BaHfO₃ and Mg₂Hf₅O₁₂, respectively. Rare earth oxides with large ionic radii usually form pyrochlore-type (P) compounds of composition Ln₂Hf₂O₇, whereas rare-earth oxides with small ionic radii combine with hafnia to form wide regions of fluorite-like solid solutions. In the region of compositions corresponding to the pyrochlore-type compounds rare-earths with the smallest ionic radii (Sc, Yb) form compounds with rhombohedral structures (R) of the composition M₄Hf₃O₁₂(M₇O₁₂). Together with the latter, compounds M₇O_11.5 and M₇O₁₁ were found for gadolinium and erbium and M₉O₁₇ and M₇O₁₃ for scandium. Most of these compounds are stable only over a certain temperature range and transform into disordered F-type cubic solid solutions at elevated temperatures. In addition, there exist limited regions of solid solutions based on the monoclinic (M) and tetragonal (T) modifications of HfO₂ as well as on various structural modifications (C, B, A, H, X) of rare-earth oxides.

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Up and down conversion photoluminescence and structural properties from hafnium doped with different lanthanides and lithium
2020, Journal of Alloys and Compounds
Citation Excerpt :
The tetragonal phase is obtained at temperatures below ∼1700 °C, and the cubic phase at ∼2200 °C, the cubic phase. The tetragonal and cubic structures of hafnium oxide have been stabilized when it is doped with different elements such as Strontium, Calcium, Barium, Magnesium, Lanthanum, Neodymium, Samarium, Dysprosium, Yttrium, Ytterbium and other elements [7, 21–25], at temperatures below 1700 °C. Due to the physical and chemical properties of hafnium oxide, is for different applications in electronics, magnetoelectronics, metal oxide semiconductors [26, 27], waveguides [28], optoelectronic devices [29], IR optical devices [30] and new scintillation materials, in resistive switching technology (CMOS) [29, 31, 32], by these reasons it is a promising material for a wide variety of scientific applications.
The structural and photoluminescent results of the lanthanum, erbium, ytterbium and lithium doped hafnium oxide phosphors; are presented. These powders were synthesized by the solvent evaporation technique, different percentages of doping of the lanthanides were carried out, obtaining monoclinic and cubic phases, also a cubic phase is present when doping lanthanides with 28% mol. Up-conversion (UC) and down-conversion (DC) luminescence spectra when excited with a 980 nm laser, three emission regions are presented; two in the visible (up-conversion) and one in the infrared (downshift), are observed. The green emission located at 528 nm, 543 nm and 559 nm; associated whit transitions of erbium ion (²H_11/2 + ⁴S_3/2) → ⁴I_15/2 and in the red emission located at 653 nm and 678 nm; associated whit transitions of erbium ion (⁴F_9/2 + ⁴I_9/2) → ⁴I_15/2. In 1532 nm, the infrared down conversion associated electronic transition ⁴I_13/2 → ⁴I_15/2 of erbium ion. The luminescence emission intensity increase in green is 336 times and in red is 105 times when doping with lithium in comparison with samples without lithium co-doped.
In the XRD diffractograms shown the monoclinic, cubic and mix of the phases in the phosphors; these are confirmed with the TEM diffraction patterns. The EDS result indicates the presence of HfO₂, Er³⁺ and Yb³⁺, in the phosphorus; hafnium decreases due to the presence of ions lanthanides. XPS showed changes in energy values due to doping of lanthanides. The CIE diagram indicates that HfO₂ doped phosphors have a variety of shades from red to yellow.
Structural, electronic and optical properties of transition metal doped Hf<inf>1-x</inf>TM<inf>x</inf>O<inf>2</inf> (TM = Co, Ni and Zn) using modified TB-mBJ potential for optoelectronic memristors devices
2020, Optik
Citation Excerpt :
Beside these dielectrics, hafnium oxide (HfO2) has great attraction and has opened a new horizon of research because of its large band-gap energy (Eg = 5.6–5.8 eV) [9,10]. At ambient pressure, HfO2 can have three phases: monoclinic (m-HfO2 with space group P21/c) at low temperature, tetragonal (t-HfO2with space group P42/nmc) at around 1700 Co, cubic fluorite (c- HfO2with space group Fm3m) at about 2600 Co [11]. However, the c-HfO2 attribute the stability by doping with bivalent or trivalent cations even at low temperature.
In the present study, we have focused to investigate the structural, electronic and optical properties of transition metal (TM) doped HfO₂ i.e; Hf_1-xTM_xO₂ (TM = Co, Ni, Zn, x = 12.5%) using the Full Potential Linearly Augmented Plane Wave (FP-LAPW) based on the density functional theory (DFT). Perdew-Burke-Ernzerhof - Generalized Gradient Approximation (PBE-GGA) has been used as an exchange correlation potential. In addition, Tran-Blaha modified Becke-Jahnson exchange potential approximation (TB-mBJ) has been employed to calculate improved electronic properties. The later approach better estimates the values of the electronic band gap much closer to the values of band gap calculated experimentally. The studies of the band structure, density of states and charge density reveal that Co-doped HfO₂ is more appropriate dopant to enhance the conductivity for resistive random accesses memory (ReRAM) devices. The results from partial density of states (PDOS) disclose the facts that localized energy states, i.e., TM-3d and O-2p have contributed mainly in increasing conductivity through hybridization. The optical analysis depicts that Hf_1-xCo_xO₂ can absorb a wide ultra violet (UV) range of electromagnetic radiations in line with the electronic behavior which has been found a most suitable candidate for ReRAM/optoelectronic memristors and other allied devices.
Structure, electronic, magnetic and optical properties of cubic Hf<inf>1-x</inf>(TM)<inf>x</inf>O<inf>2</inf> (X = 0, 0.25, TM = Mn, Fe, Co, Ni): A first principle investigation
2019, Journal of Alloys and Compounds
Citation Excerpt :
In the following section of Methodology, we first describe the details of our calculations, while in Section 3 we discuss our results and finally conclude in Section 4. At ambient pressure, HfO2 exists in three phases such as monoclinic at low temperature, tetragonal at around 2000 K, cubic at about 2900 K [33,34]. Till now monoclinic phase of c-Hafnium has been studied extensively as compared to other phases.
In the present work the structural, electronic, optical and magnetic properties of pure cubic HfO₂and 3d transition metal (Mn, Fe, Co, Ni) doped (Hf_1-xTM_xO₂) alloys (x = 0.25%) have been investigated by Density Functional Theory (DFT) as implemented in the FP-LAPW (full-potential augmented plane wave plus local orbital's) method employing generalized gradient approximation (GGA) and TB-mBJ exchange correlation methods. The calculated results such as lattice parameters and band gap are in good agreement with available experimental results. The calculation indicates that Hf_1-xTM_xO₂ with x = 0 is a symmetric band gap semi-conductor but as a result of 3d TM doping, the band structure changes dramatically, presenting the half-metallic nature for all Hf_1-x(TM)_xO₂ (x = 0.25, TM = Mn, Fe, Co, Ni) with majority spin states (spin up) as metallic and minority spin states (spin down) as semi-conducting for TM = Mn, Fe, Co and for TM = Ni the majority spin states (spin up) as semi-conducting and minority spin states (spin down) as metallic. The main contributions to the magnetic moment are mainly from the doped transition metals,TM = Mn, Fe, Co and Ni atoms with partial moments of 3.67 μB, 4.08 μB, 2.36 μB and 2.16 μB, respectively. From the charge density contour plots it was found that Hf_0.75TM_0.25O₂ compounds have merged ionic and covalent character for the Hf–O and TM–O bonds. Further we have also explored the optical properties like reflectivity, index of refraction, energy loss, optical spectrum (absorption spectrum) corresponding to the imaginary part of dielectric function in the range 0–30 eV.
Synthesis of HfO<inf>2</inf> from hafnium hydroxide hydrate
2019, Journal of Alloys and Compounds
A comprehensive study of processes taking place during synthesis and subsequent thermal treatment of hafnium oxide was performed. Synthesis of HfO₂ involves following stages: stepwise dehydration of hydrated hafnium hydroxide, crystallization of metastable tetragonal phase of HfO₂ and subsequent irreversible transition to the stable monoclinic modification. Preliminary heat treatment lowered temperature of crystallization of HfO₂ and resulted in changing process mechanism.
First-principles studies on mechanical properties and band structures of TMO <inf>2</inf> (TM = Zr or Hf) nanostructures under high pressure
2019, Physica B: Condensed Matter
Citation Excerpt :
Zirconia (ZrO2) and Hafnia (HfO2) are transition metal oxides that have been extensively studied due to their technological importance. These materials are mainly used in fuel cells [1–4], catalyst [3,5] and as an alternate in gate dielectric material to replace SiO2 in metal oxide semiconductor ﬁeld-effect transistor (MOSFET) [4,6] owing to their excellent chemical, thermal, mechanical and dielectric properties. The chemical and physical properties of both ZrO2 and HfO2 are similar in many ways.
The mechanical and band structure studies of TMO₂ (TM = Zr or Hf) nanostructures under high pressure in the range of 0 GPa and 50 GPa is studied using density functional theory. Upon applying the pressure, the unit cell size decreases for TMO₂ nanostructures. The Young's and bulk modulii of TMO₂ decreases until 30 GPa and then increases up to 50 GPa. The universal anisotropy increases with the increase in the pressure. The ZrO₂ and HfO₂ nanostructure turns from ductile to brittle nature for the applied pressure beyond 30 GPa, which is inferred from Pugh's criterion. The band gap of TMO₂ increases with the increase in the applied pressure. The findings show the various transformations of TMO₂ nanostructures under high pressure, which can be used for tailoring the band gap and mechanical properties of TMO₂ nanomaterials.
First-principles calculations of electronic and optical properties of F, C-codoped cubic HfO<inf>2</inf>
2015, Journal of Magnetism and Magnetic Materials
First-principles calculations based on DFT+U were performed on electronic and optical properties of F, C-codoped cubic HfO₂. The calculations show that strong 2p–2p/5d admixtures result in half-metallic ferromagnetism behaviors of F, C-codoped cubic HfO₂. Both the direct 2p–2p interaction and the indirect 2p–5d/2p–2p coupling interactions can be expected to contribute to the long-range magnetic coupling. Meanwhile, F and C codoping induces obvious increase of refractive index and new steep absorption peaks at lower energy region ∼2.8 eV, which can be used for photoabsorption applications.

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PaperHfO2-based refractory compounds and solid solutions: 2. Kinetics and mechanism of compound formation in the systems HfO2M2O3 (MO)

Abstract

Mat. Res. Bull.

Zhurn. Neorgan. Khim.

Zhurn. Prikl. Khim.

Electrochemistry of Fused Salts and Solid Electrolytes

X-Ray Diffraction of Mineral Deposits

Izv. Akad. Nauk SSSR, ser. Neorgan. Mater.

Zhurn. Neorgan. Khim.

Izv. Akad. Nauk. SSSR, ser. Neorgan. Mater.

Phase Relations and Physical-Chemical Properties of Solid, Solutions in the Systems HfO2DyO1.5PrOx and HfO2MgO

Zhurn. Neorgan. Khim.

Dokl. Acad. Nauk. SSSR

Electrochemistry of Fused Salt and Solid Electrolytes

Izv. Akad. Nauk SSSR, ser. Neorgan. Mater.

Izv. Akad. Nauk SSSR, ser. Neorgan. Mater.

Zhurn. Strukt. Khim.

Dokl. Akad. Nauk SSSR

Compt. Rend.

Rev. Int. Hautes Temp. et Refract.

Mat. Res. Bull.

Izv. Akad. Nauk SSSR, ser. Neorgan. Mater.

Izv. Akad. Nauk SSSR, ser. Neorgan. Mater.

Izv. Akad. Nauk SSSR, ser. Neorgan. Mater.

Paper
HfO₂-based refractory compounds and solid solutions: 2. Kinetics and mechanism of compound formation in the systems HfO₂M₂O₃ (MO)

Phase Relations and Physical-Chemical Properties of Solid, Solutions in the Systems HfO₂DyO_1.5PrO_x and HfO₂MgO