HAL Id: jpa-00215383
https://hal.archives-ouvertes.fr/jpa-00215383
Submitted on 1 Jan 1973
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
STUDY OF THE REORIENTATION OF
Mn2+-VACANCY COMPLEXES IN POTASSIUM CHLORIDE
A. Brun, P. Dansas
To cite this version:
A. Brun, P. Dansas. STUDY OF THE REORIENTATION OF Mn2+-VACANCY COMPLEXES IN POTASSIUM CHLORIDE. Journal de Physique Colloques, 1973, 34 (C9), pp.C9-61-C9-62.
�10.1051/jphyscol:1973908�. �jpa-00215383�
STUDY OF THE REORIENTATION OF Mn2+-VACANCY COMPLEXES IN POTASSIUM CHLORIDE
A. BRUN
Laboratoire de Physique Electronique, B i t . 220, UniversitC Paris-Sud, Centre d'Orsay, 91405 Orsay, France
P. DANSAS (*)
Laboratoire de Physique de la Matitre Condensee, Parc Valrose, 06034 Nice. France
RbsumC. - L'analyse simultanee des resultats obtenus a partir des mesures de thermocourants de depolarisation et de RPE nous permet de proposer un modele pour la reorientation des complexes lacune-impurete dans KC1 : MnZr. Les trois premiers Ctats energetiques de ces complexes sont determines a partir des mesures de RPE et confirmes par les resultats de conduc- tivite. A partir des mesures de thermocourants, on peut identifier la barriere d'energie qui gouverne la reorientation des complexes.
Abstract. - Depolarization thermocurrent and EPR measurements have been performed on Mnzi doped KC1 crystals. From these, we derived a model for the impurity-vacancy complexes reorientation and the binding energies of the first three associated states. One of the two thermo- current peaks is ascribed to the next nearest neighbour-nearest neighbour vacancy jump, the other to aggregates.
Polarization phenomena resulting from the reorien- tation of the (( dij~oles )) wliicli arise from the inipurity- vacancy complexes (IV) formed when divulent impu- rities are incorporated substitutionally in a n alkali halide lattice are experimentally studied here in M n 2 + doped KC1 crystals by means of tlie ionic tliel-mocur- rent method (ITC).
The basic experiments whose ~inalysis h ~ t s led to the present results are reported in tlic Joiirilcil of' Plij~sic.~
arid C11en1isti.j. o/'SolirlLs ( t o the published).
After annealing nt 700 0C in controlled atmo- sphere, tlie samples are cluenclied at liclilid nitrogen temperature ; we observe two ITC bands wit11 dilTe- 'rent decrease kinetics : i t means that these two bands are not due to defects of the same kind.
From the comparison of tlie decrease kinetics o f tlie I T C bands with the one of' the two E P R spectra I l l , and 111, (using Wittkins' ~iotations. 1959) due to M n 2 + with a positive ion vacancy in the nearest and the next-nearest cation site respectively, a band is ascribed to IV dipoles. A n energy value of 0.49 eV can be associated to this bancl. The other band is ascribed to aggregates.
( * ) Present addrcbi : Lnboratoirc cle Pliyhicluc Electl.onicl~~e.
Bit. 220, Universiti. P;~r.i.;-Sucl, ('cntl-c d'0ri;i). c)1105 01-{a!.
France.
A three-neiglibour shells model for tlie vacancy around tlie inipurity ion is used in order to perform the IV complexes reorientation mechanisnl study.
In the first place, tlie energies of association of tlie divalent cation impurity-cation vacancy pairs in tlie first three associated states must be ev:~luated.
The Maxwell-Boltzma~i~~ distribution of IV com- plexes is calculated and compared at dilTerent tempe- ratures with the relative intensity measurements of the extreme lines observed in the I l l , a n d 111, E P R spectra.
The binding energies of the nearest-neiglibo~~r [C2,(1, I , O)], 1;ext-nearest neighbour [C,,(2. 0, 0)]
and third-nearest-neighbour [C,(2, 1 , I ) ] M n 2 + - K i ~ vacancy pairs are found to be - 0.43. - 0.46 and
- 0.37 eV respectively (binding enel-2ies of the others pairs are taken equal with the Coulonlb energies o f association). It is concluded that the second-associati011 sate is tlie deepest one.
Likewise. a n average association cnergy value o f 0.48 + 0.10 eV for the first two associated states has
- 0.05
been derived from cond~~ctivity mc:tsurclnents. A n enthalpy of solution /I, is also dctermincci u~itli better uccul-;icy : /I, = 0.79 el'. proving :I slight solu- bility of Mn' ' ions.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973908
C9-62 A. B R U N P.
Then, using the three-shells model, we derived four relaxation modes.
Though the ITC technique is very sensitive only one of these is experimentally observed. That leads us to the following conclusions :
- the energy barrier of the jump frequency for the interchange between a nearest neighbour potassium ion and a nearest neighbour vacancy (or for the direct interchange of the divalent impurity ion and a nearest
DANSAS
neighbour vacancy) is greater than the other energy barriers,
- the experimentally determined reorientation activation energy (0.49 eV) is ascribed to the energy barrier for the jump of a next nearest neighbour vacancy to a nearest neighbour site (I).
( I ) For a detailed account of these results, refer to cc A. Brun,
P. Dansas and F. Benitre n, J. Phys. & Chem. Solids (to be published).
