Charge and magnetic states of rutile TiO2doped with Cr ions

Kim, Rokyeon; Cho, Suyeon; Park, Won Goo; Cho, Deok‐Yong; Oh, Seung Cheol; Saint-Martin, R.; Berthet, P.; Park, Je‐Geun; Yu, Jaejun

doi:10.1088/0953-8984/26/14/146003

Cited by 10 publications

(3 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Kim et al . 45 stated that Cr 3+ defects in rutile TiO 2 are promoted when the samples are grown under oxygen poor conditions and determined that the formation energy of V O 2+ and Cr 3+ is smaller than the formation energy of Cr 4+ . Taking into account that the formation energy of V O 2+ is also smaller than V O 1+ and V O 0 33 , 35 , it is expected that the preferential oxidation state of Cr in TiO 2 should be Cr 3+ .…”

Section: Resultsmentioning

confidence: 99%

Understanding the effects of Cr doping in rutile TiO2 by DFT calculations and X-ray spectroscopy

Vásquez

Maestre

Cremades

et al. 2018

Sci Rep

View full text Add to dashboard Cite

The effects of Cr on local environment and electronic structure of rutile TiO2 are studied combining theoretical and experimental approaches. Neutral and negatively charged substitutional Cr impurities CrTi0 and CrTi1− as well as Cr-oxygen vacancy complex 2CrTi + VO are studied by the density functional theory (DFT) within the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) functional. Experimental results based on X-Ray absorption spectroscopy (XAS) and X-Ray photoelectron spectroscopy (XPS) performed on Cr doped TiO2 at the Synchrotron facility were compared to the theoretical results. It is shown that the electrons of the oxygen vacancy tend to be localized at the t2g states of the Cr ions in order to reach the stable oxidation state of Cr3+. Effects of Cr on crystal field (CF) and structural distortions in the rutile TiO2 cell were analyzed by the DFT calculations and XAS spectra revealing that the CF and tetragonal distortions in TiO2 are very sensitive to the concentration of Cr.

show abstract

Section: Resultsmentioning

confidence: 99%

Understanding the effects of Cr doping in rutile TiO2 by DFT calculations and X-ray spectroscopy

Vásquez

Maestre

Cremades

et al. 2018

Sci Rep

View full text Add to dashboard Cite

show abstract

“…On the basis of DFT and the formation energy calculations taking into account a supercell, the presence of two Cr 4+ defects in oxygen-rich conditions gives rise to ferromagnetic coupling, whereas the occurrence of Cr 3+ pairs associated with oxygen vacancies in oxygen-poor conditions leads to paramagnetic interactions. 10 To the best of our knowledge, the occurrence of ferromagnetic coupling in Cr-doped cassiterite 11−14 can only be explained by the presence of Cr 4+ or electrons trapped in the lattice due to oxygen defects, in interaction with other paramagnetic centers such as Cr 3+ or Cr 4+ . 15−18 The low solubility of Cr 3+ may be related to its lower ionic size (0.62 Å in an octahedral site) compared to that of Sn 4+ (0.69 Å), generating a more ionic bond and inducing oxygen defects into the rutile lattice, with octahedral sites sharing edges or faces, creating constraints.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Cr^IV/Cr^III Valence States in Purple Cr-Doped SnO₂ Nanopowders: The Key Role of Cr^IV Centers and Defects

et al. 2019

View full text Add to dashboard Cite

A low content of chromium (≤5 mol %) has been incorporated into a SnO 2 cassiterite by a coprecipitation route in a basic medium, followed by an annealing step under an O 2 flow at T = 800°C and T = 1000°C. Accurate UV−vis and EPR spectroscopy investigations show the coexistence of isolated Cr 4+ and Cr 3+ ions as well as ferromagnetic Cr 4+ −Cr 3+ and antiferromagnetic Cr 3+ −Cr 3+ interactions. The strong purple hue is related to the isolated Cr 4+ ions stabilized in a distorted octahedral site. This is thanks to the second-order Jahn−Teller (SOJT) effect with a crystal field splitting 10Dq value around 2.4 eV, whereas the 10Dq value is around 2 eV for isotropic Cr 3+ ions, partially substituted for Sn 4+ ions in cassiterite. Just after the coprecipitation process, only Cr 3+ species are stabilized in this rutile network with a poor crystallinity. The isolated Cr 4+ content remains high after annealing at 800°C for 2 days especially for the highest Cr rate (2 and 5 mol %), leading to a darker purple color, but unfortunately the Cr 3+ content also increases for a higher Cr concentration. A lighter purple hue can be reached after calcination at a higher temperature (T = 1000°C) for a shorter time (4 h) but with a lower Cr content to avoid Cr clusters. This is due to stabilizing a high content of isolated Cr 4+ species and limiting the Cr 4+ −Cr 3+ ferromagnetic interactions, which are optimal for a 2% Cr content and also cause the color to darken. The key roles of the Cr 4+ rate and the Cr 4+ −Cr 3+ clusters create local defects whose concentration strongly varies with a total Cr content, which have then been demonstrated to strongly influence the optical and magnetic properties.

show abstract

“…TiO 2 包括三种晶相, 分别是锐钛矿相、金红石相及板钛矿相, 其中锐钛矿TiO 2 的研究最为广泛 [5] . 2001年, Matsumoto等 [6] 首次在实 1) 磁性是本征体自身具有, 如: 实验上采用溶剂加热法将Ni掺入TiO 2 纳米粒子 [7] 和利用湿化学法将Co掺入TiO 2 纳米粒子中 [8] , 结果显示未掺杂体系的磁化强度值更高, 这说明磁性来源于本征体自身; 2) 磁性来源于掺杂元素, 如: Mn掺杂TiO 2 [9] 、N 掺杂TiO 2 [10] 、Cr掺杂TiO 2 [11] 结果表明: Ti 1x Mn x O 2 薄膜在室温下表现出铁磁有序性, N-TiO 2 体系的磁性来源于N-2p态, Cr-TiO 2 体系中Cr 3+ 为Curie-…”

unclassified

First principle study of influence of transition metal (Cr, Mn, Fe, Co) doping on magnetism of TiO2

王少霞¹,

赵旭才²,

潘多桥³

et al. 2020

Acta Phys. Sin.

View full text Add to dashboard Cite

It is still in controversy whether the transition metal doped TiO2 will generate room temperature ferromagnetism and where its magnetism originates from. In order to solve this problem, in this paper we use the GGA+U method based on density functional theory to conduct a first-principle study of the magnetic and optical properties for each of the systems of Ti0.875X0.125O2, X = Cr, Mn, Fe, Co. We calculate the ground state energy of each system, on the supposition that they are ferromagnetic or antiferromagnetic. After comparison, the ferromagnetic state is speculated to be its ground state. The binding energy and magnetism calculation results show that Ti0.875Cr0.125O2 has the best stability in all doped systems, that the transition metal element doped TiO2 system has a net magnetic moment, and that the doped systems are ferrimagnetic. In comparison, the net magnetic moment produced by Cr, Mn and Fe doped with TiO2 are substantial, showing that these three systems have good ferromagnetic properties. The Curie temperatures of all doped systems are above room temperature, which is of great significance for the electron spin to retain the information in dilute magnetic semiconductors (DMS), and also greatly helps with the practical application of magnetic materials. The analysis of the energy band structure reveals that intrinsic TiO2 is non ferromagnet, Ti0.875Cr0.125O2 and Ti0.875Mn0.125O2 maintain semiconductor properties, and Ti0.875Fe0.125O2 and Ti0.875Co0.125O2 exhibit metal characteristics. The doped systems produce room temperature ferromagnetism, the main magnetic source is the transition metal elements (Cr, Mn, Fe, Co) 3d electron orbit induced polarization of the surrounding O-2p state spin electrons, causing the systems to produce a net magnetic moment and be ferromagnetic. The absorption spectrum of the doped system is red-shifted, which shows that the doping causes the range of its absorption spectrum to extend to the visible range. At the same time, in all the doped systems in this article, Fe and Co doped TiO2 have the best light absorption intensity, and the magnetic property of the Fe doped system is the strongest, which indicates that when the system is ferromagnetic, the spin up and spin down splitting will occur in the local magnetic field, which will change the electronic structure of TiO2 and enhance its photocatalytic performance. The calculation results in this paper are of theoretical significance for preparing TiO2 with curie temperature above room temperature by being doped with transition metal elements of Cr, Mn, Fe, and Co.

show abstract

Charge and magnetic states of rutile TiO₂doped with Cr ions

Cited by 10 publications

References 25 publications

Understanding the effects of Cr doping in rutile TiO2 by DFT calculations and X-ray spectroscopy

Understanding the effects of Cr doping in rutile TiO2 by DFT calculations and X-ray spectroscopy

Tuning the Cr^IV/Cr^III Valence States in Purple Cr-Doped SnO₂ Nanopowders: The Key Role of Cr^IV Centers and Defects

First principle study of influence of transition metal (Cr, Mn, Fe, Co) doping on magnetism of TiO<sub>2</sub>

Contact Info

Product

Resources

About

Charge and magnetic states of rutile TiO2doped with Cr ions

Cited by 10 publications

References 25 publications

Understanding the effects of Cr doping in rutile TiO2 by DFT calculations and X-ray spectroscopy

Understanding the effects of Cr doping in rutile TiO2 by DFT calculations and X-ray spectroscopy

Tuning the CrIV/CrIII Valence States in Purple Cr-Doped SnO2 Nanopowders: The Key Role of CrIV Centers and Defects

First principle study of influence of transition metal (Cr, Mn, Fe, Co) doping on magnetism of TiO<sub>2</sub>

Contact Info

Product

Resources

About

Charge and magnetic states of rutile TiO₂doped with Cr ions

Tuning the Cr^IV/Cr^III Valence States in Purple Cr-Doped SnO₂ Nanopowders: The Key Role of Cr^IV Centers and Defects