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influence of impurities on physical properties of crystals SBN

Presence of hollows in crystalline structure of type of tungsten bronze allows to enter wide enough gamut of impurities: from ions of the transitive metals to rare-earth ions. The doping of crystals SBN impurities of rare-earth devices (Se, Cr, Rh, to It, Nd and others) changes the dielectric properties, increments piezoelectric and linear electrooptical coefficients at a room temperature [17, 38, 51, 59, 72, 74, 85-92].

By means of the nejtronno-active analysis it has been erected, that 3+должны to be the most probable situation of ions Se channels A1, it replaces atoms of strontium in positions Sr (I) [51, 87], and ions Cr3+садятся on places - Nb5 + [88]. The charging state 3 + for ions Se has been spotted from X-ray photoelectric spectroscopy [89], and for ions Sg - from measurings of a photoconduction [88]. Like ions Сг3 +, ions Rh3 + and Еи3 + rank Nb5 + in an octahedron [93, 94]. Proceeding from affinity of the ionic radiuses Sr2 + (ri=1.44) and Се3 + (ц=1.34 A), Nb5 + (ц=0,64) and Сг3 + (ц=0,74), authors guess, that at introduction in matrix SBN of tervalent atoms Se there is the heterovalence replacement. The difference of charging states between impurities and the exchanged ions, leads to formation of a redundant charge, in a consequence of that there is a local strain of a lattice and, as consequence, there is a change of a local field of a crystal [89] which polarises off-centre impurities in casual directions. Thus, the presented effects show display in alloyed crystals SBN of casual fields. Occurrence
Polarised impurities, in an end result leads to a dielectric dispersion depending on temperature [67, 85, 93 - 97] and to depression Tm ε.

Authors [76] with use of atomno-power microscopy have shown, that, introduction of the impurity ions Се3 +, the labile superficial charge which migrates under the influence of an exterior electric field is voided. During too time, introduction in SBN:61 small amount Se 3 + (~ 0,05 pier. %) does not lead to any appreciable changes of allocation of divalent cations in vacuities three-dimensional kislorodnoyooktaedricheskogo a skeleton [51].

In operation [85] it is scored, that the temperature of a maximum of an inductivity decreases from 80°С in pure SBN61 to a room temperature for crystals SBN61 alloyed by impurities with concentrations (Se, Sg, or both) ≈ 20 000 ppm. It is shown, that an inductivity maximum thus ushirjaetsja in the impurity crystals SBN:Ce, Sg in comparison with not alloyed (fig. 1.22). Value of an inductivity of the impurity crystals SBN [95] As a result increases.

According to [72], introduction of impurity Rh and to It leads to magnification of values of an inductivity, in comparison with similar values for pure crystal SBN. Doping Rh of crystals SBN does not lead to detrusion of temperature of a maximum of an inductivity, at the same time value of an inductivity depends on concentration of an impurity: with magnification of concentration Rh value of an inductivity increases (fig. 1.23). Introduction of an impurity leads to It to bias of a standing of temperature of a maximum of an inductivity in field of low temperatures, with magnification of concentration to It value of an inductivity decreases (fig.

1.24).

Fig. 1.22. Dependence of an inductivity on temperature of crystals SBN with various concentrations: () - Se, () - Sg [85].

Fig. 1.23. Temperature dependence of an inductivity of crystals SBN: 1 pure, 2 - lOOppm Rh, 3 - 500ppm Rh, 4 - 2000ppmRh [72].

Fig. 1.24. Temperature dependence of an inductivity of crystals SBN: 1 pure, 2 - 2000ppmEu, 3 - 4000ppmEu, 4 - 8000ppmEu, 5 - 16000ppmEu [72].

If impurities Sg, Se and small impurities Rh in crystals SBN lead to reduction of values of spontaneous polarisation and a coercive field an impurity to It and major (2000ppm) concentration of impurity Rh increment spontaneous polarisation, but reduce value of a coercive field [72]. In crystals SBN with higher impurity concentration Se, Sg and Rh the loop of the dielectric hysteresis with magnification of temperature to Ttah maintains a view saturated [73]. At the further magnification of temperature above Gah quantity of polarisation decreases, the loop does not disappear, and becomes extended, i.e. in a crystal polarisation is maintained to order temperatures 110°С (fig. Е25). Sharp reduction of polarisation is observed at the temperatures exceeding Etah approximately on 15-17 ° in all explored samples, irrespective of a view and an impurity concentration. Such temperature dependence of polarisation speaks that at a crystal with dim phase transition local fields of ferroelectric phases can be maintained in a wide temperature interval.

Fig. 1.25. Loops of the dielectric hysteresis in crystal SBN:Rh 0.2 at. % at temperatures 30 (' (With (70°С (), 100°С (). [73]

Examinations of the dielectric properties of crystals SBN alloyed Se, Sg, Rh and to It, has shown, that the breadth of field Kjuri does not change at introduction in crystal SBN of impurities Se, Rh and to It major (16000ppm) concentrations, however is incremented at introduction of impurity Sg and decreases at small concentration (to 8000ppm) impurities to It (Tables Е2 and EZ) [72].

Table 1.2

SBN pure Se, (at. %) Sg, (at. %)
depolja -

rizov.

Odes 0,4 0,8 0,3 1,0 4,0
Tmax0C 84 74 60 50 73 47 -14
ε (Tmax) 5300 26000 21000 13000 22000 14000 7600
Θ 17 14 13 13 14 21 31

Table 1.3

SBN Rh, (at. %) To it, (at. %)
0,01 0,05 0,2 0,2 0,4 0,8 1,6
i°C 85 84 85 80 77 69 56
S (Tmax) 10000 10000 13000 38200 39900 33500 28700
0 16 16 15 10 11 11 16

According to authors [82], ions of impurities in crystals SBN are flaws which create centres of fastening of domain boundaries - piningovye points. In crystals SBN:Ce ions Се3 + are deep piningovymi centres. Very strong piningovye forces actively kill the internal fields arising because of the disorder of local charges. It causes delayed dynamics of polarisation in ferroelectric and in paroelektricheskoj to a phase, and maintenance of domain structure approximately on 30 To above Tm ε [82].

Introduction of a tervalent ion of chrome to the place of five-valence niobija shapes oxide-coated vacancies [98]. Inner-shell electrons are cancelled by electron defects and-or oxide-coated vacancies, reducing a dark conduction and a photoconduction [99]. It was revealed, that, since impurity level
The chrome, equal 0,51 at. %, the photoconduction linear relation to become holographic storage approaching for record.

The disordering peculiar to crystals SBN bearing responsibility for casual fields in a crystal, does not change considerably at introduction of impurities, not looking that impurities import an additional disordering in a charge and promote formation of fields with local polarisation.

1.5.

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A source: Lisitsyn Vladimir Sergeevich. PYROELECTRIC PROPERTIES And the STATE of POLARIZATION of MONOCRYSTALS of FIRM SOLUTIONS NIOBATA of BARIUM of STRONTIUM And NIOBATA CALCIUM BARIUM. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver - 2015. 2015

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