# High temperature x-ray diffraction studies on Cr-doped V2O3☆

TL;DR: In this article, the room temperature rhombohedral structure of (Cr 0.01V0.99)2O3 has been determined at different temperatures from the relative X ray intensities.

About: This article is published in Materials Research Bulletin.The article was published on 1974-06-01. It has received 7 citations till now. The article focuses on the topics: Atmospheric temperature range & Powder diffraction.

##### Citations

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TL;DR: In this article, the Debye (D)−Einstein (E) function was used to evaluate the lattice heat capacity of pure and doped V2O3.

29 citations

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TL;DR: Chromium-doped vanadium sesquioxide, (V1−xCrx)2O3, displays two metal-insulator transitions with temperature for 0.005 as mentioned in this paper.

16 citations

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TL;DR: In this article, the high-temperature X-ray structure of (CrxV1−x)2O3 phases (withx < 0.10) has been studied.

12 citations

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TL;DR: In this paper, a phase diagram for the dilute V2O3-Al 2O3 alloy system is presented and the role of Cr3+ and Al3+ as a dopant in the lattice is briefly discussed.

Abstract: Measurements of the entropy change are reported for the high-temperature metal-insulator (MI) transitions in the (V1−xCrx)2O3 and (V1−xAlx)2O3 systems. It is emphasized that the entropy of the I phase exceeds that of the M phase. Evidence is presented to show that the M and I phases coexist over a narrow temperature range. The transformation is attended by enormous hysteresis effects; these indicate that the lattice plays an important role in the transition. The probable role of Cr3+ and Al3+ as a dopant in the V2O3 lattice is briefly discussed. A phase diagram for the dilute V2O3-Al2O3 alloy system is presented.

6 citations

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TL;DR: In this paper , the authors investigated the strain effects on the metal-insulator transition (MIT) in thin films and the mechanisms behind them are not yet fully understood, and they highlighted the importance of trigonal distortion to understand the MIT in the VC1 thin films.

Abstract: ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ is an archetypical Mott material which exhibits Cr doping and/or temperature-induced paramagnetic metal to paramagnetic insulator/antiferromagnetic insulator (PM-PI/AFI) transitions. However, the strain effects on the metal-insulator transition (MIT) in thin films and the mechanisms behind them are not yet fully understood. In this study, we investigate the strain effects on the MIT in $({\mathrm{V}}_{0.99}{\mathrm{Cr}}_{0.01}{)}_{2}{\mathrm{O}}_{3}$ (VC1) thin films growing on $c$-plane (001), $r$-plane (012), and $a$-plane (110) ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates. The strains can be tuned in a wide range over 1% in $\mathrm{VC}1\text{/}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ thin films by changing the substrate temperature. Remarkably, the influence of strain on the MIT differs dramatically from (001)-oriented and non-(001)-oriented $\mathrm{VC}1\text{/}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ thin films. The PM-PI transition can be effectively modulated by strain tuning in the (001) $\mathrm{VC}1\text{/}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ thin films accompanied by gradual transformation from the PM/PI phase into the AFI phase upon cooling. On the contrary, both (012) and (110) $\mathrm{VC}1\text{/}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ thin films exhibit sharp PM-AFI transitions irrespective of the strain states. The orientation-dependent strain effects on the MIT in the $\mathrm{VC}1\text{/}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ thin films could be explained by the trigonal distortion within electronic correlation scenario. The trigonal distortion of $\mathrm{V}(\mathrm{Cr}){\mathrm{O}}_{6}$ octahedra along (within) the $c$ axis ($ab$ plane) in the (001) $\mathrm{VC}1\text{/}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ thin films can be directly modulated by the strains. However, the trigonal distortion in the (012) and (110) $\mathrm{VC}1\text{/}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ thin films would hardly be affected due to the deviation of the film orientation from the $c$ axis. This explanation is experimentally confirmed by Raman spectra as a sensitive probe of the trigonal distortion in VC1 thin films. These results highlight the importance of trigonal distortion to understand the MIT in the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ compound.

5 citations

##### References

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Bell Labs

^{1}TL;DR: In this paper, the effect of impurity ions in terms of the changes they cause in the bandwidth was discussed in analogy with the effects of pressure, and it was shown that the residual resistivity of metallic ions is strongly impurity dependent.

Abstract: The addition of ${\mathrm{Ti}}^{3+}$ and ${\mathrm{Mg}}^{2+}$ to ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ leads to the suppression of the antiferromagnetic insulating phase; whereas the addition of ${\mathrm{Ti}}^{4+}$, ${\mathrm{Zr}}^{4+}$, and ${\mathrm{Fe}}^{3+}$ results in a first-order transition from a metallic to an insulating state. The effect of impurity ions is discussed in terms of the changes they cause in the bandwidth in analogy with the effect of pressure. The Hall coefficient of metallic ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ at 4.2 \ifmmode^\circ\else\textdegree\fi{}K and 20 kbar is ${R}_{H}=+(3.5\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{3}$/C which is close to the value measured at 150 \ifmmode^\circ\else\textdegree\fi{}K and 1 atm. The residual resistivity of metallic ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ is strongly impurity dependent (140 \ensuremath{\mu}\ensuremath{\Omega} cm/at.% Cr and 35 \ensuremath{\mu}\ensuremath{\Omega} cm/at.% Ti). These results are not completely consistent with current theories for the metal-insulator transition in ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ but the best available model still seems to involve a localized-to-nonlocalized transition within the $d$ band primarily involving orbitals in the basal plane.

327 citations

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Bell Labs

^{1}TL;DR: The metal-insulator phase boundary terminates at a critical point in the $P\ensuremath{-}T$ plane, in accordance with the earlier prediction as discussed by the authors, and the discontinuous resitance drop at the transition point progressively diminishes with temperature and beyond a certain critical temperature, depending upon the Cr concentration, vanishes altogether.

Abstract: The metal-insulator (M-I) transition in Cr-doped ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$, which has been shown to be a Mott transition, was investigated by following the resistance as a function of pressure at temperatures above 298 \ifmmode^\circ\else\textdegree\fi{}K. This study has shown that the M-I phase boundary terminates at a critical point in the $P\ensuremath{-}T$ plane, in accordance with the earlier prediction. The discontinuous resitance drop at the transition, which is about two orders of magnitude at 298 \ifmmode^\circ\else\textdegree\fi{}K, progressively diminishes with temperature and beyond a certain critical temperature, depending upon the Cr concentration, vanishes altogether. Above the critical temperature only a smooth but somewhat anomalous change in resistance is seen. The critical pressure and temperature for ${({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x})}_{2}{\mathrm{O}}_{3}$ with $x=0.0375$, $x=0.0187$, and $x=0.0135$ were determined as 12.5 kbar, 390 \ifmmode^\circ\else\textdegree\fi{}K; 5.5 kbar, 433 \ifmmode^\circ\else\textdegree\fi{}K; and 3.5 kbar, 443 \ifmmode^\circ\else\textdegree\fi{}K, respectively. A straight-line extrapolation of these data yields ${P}_{c}=\ensuremath{-}1.5\ifmmode\times\else\texttimes\fi{}0.2$ kbar and ${T}_{c}=(474\ifmmode\pm\else\textpm\fi{}5)$ \ifmmode^\circ\else\textdegree\fi{}K for pure ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$. The high-temperature resistance anomaly in pure ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ near 500-600 \ifmmode^\circ\else\textdegree\fi{}K is due to supercritical behavior. X-ray studies at atmospheric pressure on Cr-doped samples with $x=0.0137$ to $x=0.004$ show that the $\ensuremath{\Delta}\mathrm{V}$ associated with the M-I transition decreases with increasing temperature and finally vanishes near about $x=0.005$. The behavior is exactly analogous to the $\ensuremath{\gamma}\ensuremath{-}$ to $\ensuremath{\alpha}\ensuremath{-}\mathrm{C}\mathrm{e}$ phase boundary which is known to terminate at a critical point. Indeed the M-I transition in Cr-doped ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ and the $\ensuremath{\gamma}\ensuremath{-}$ to $\ensuremath{\alpha}\ensuremath{-}\mathrm{C}\mathrm{e}$ transition have many similarities, and these are discussed.

100 citations

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Bell Labs

^{1}TL;DR: In this article, structural refinements of single crystals of V 2 O 3, and (V 0.962 Cr 0.038 ) 2 O3, by X-ray diffraction techniques show an increase in the short vanadium-vanadium distances at the transition, while the vanadiumoxygen distances remain essentially unchanged.

93 citations