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On the determination of inclusions in crystals grown from aqueous solutions
Journal of Crystal Growth 72 (1985) 743—744 North-Holland, Amsterdam
743
LETITER TO THE EDITORS ON THE DETERMINATION OF INCLUSIONS IN CRYSTALS GROWN FROM AQUEOUS SOLUTIONS H. LOOSER, M. EHRENSPERGER and H. AREND Laboratory of Solid State Physics, Swiss Federal Institute of Technology, CH- 8093 Zurick Switzerland Received 3 June 1985
Growth solution inclusions were determined in gel grown PbHPO
4 crystals by means of differential scanning calorimetry. The
detection limit corresponds to 20 ppm H 20.
A characteristic imperfection in solution grown crystals are inclusions of the mother solution from which the crystals wee grown. Even small amounts of such inclusions, which are sometimes difficult to detect, can drastically influence important properties of their “host” crystal. Such effects were observed, e.g., in non-transparent 2 Pt(CN4)Br04 3.2H2O crystals where an extremely high mobility of Br ions was erroneously deduced from NMR signals due to Br ions in aqueous solution inclusions [1,2]. Recently Nelmes and Lockwood detected anomalous transition-like effects in PbHPO4 I
3.0
I
I
I
slightly below 273 K, in addition to the well known para-ferroelectric phase transition at 308 K [3]. Differential scanning calorimetry (DSC) scans of gel grown crystal platelets revealed typical peaks of a phase transition (fig. 1) in this temperature range. The phase transition was of first order, as could be deduced from a strong hysteresis effect in heating and cooling runs. In order to elucidate the nature of this effect the following experiments were made: (1) A series of about 10 samples weighing from 78 to 144 mg were examined and the intensity of the effect varied from sample to sample. I
-
~: ~ 230
250
270 290 Temperature [K]
310
330
Fig. 1. DSC scan of a gel grown PbHPO4 crystal. Scan rate 5.0 K/mm, crystal weig~it144 mg, 7~= 309 K, T~’(anomalous transition) = 269 K.
0022-0248/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
744
H. Looser et aL
/
Determination ofinclusions in crystals
(2) In PbDPO4 crystals, in which the para-ferroelectric transition is strongly shifted to higher temperatures, only a negligible shift of the anomalous effect was observed. (3) Upon heating to 450 K for 1 h the anomalous peak disappeared. These results are clear evidence that the additional peaks are due to solution inclusions. From the transition enthalpy one can calculate the amount of solvent in the crystals. The smallest amount which we were able to detect in any sample by means of a Perkin-Elmer DSC2 calorimeter corresponds to 1 ~tg or 20 ppm by weight.
Thus it is evident that differential scanning calorimetry is a very useful tool for the detection of even small amounts of aqueous solution inclusions. The described technique demands however the use of small samples with dimensions limited by the type of the measuring cell used.
References [1) H. Nagasawa and N. Miyauchi. Phys. Status. Solidi (b) 71 (1975) 671. . [2] D. Bnnkmann, G. Finger and H. Arend, Phys. Status Solidi (b) 83 (1977) 1(45. [3] R. Nelmes and D.J. Lockwood, private communication.
743
LETITER TO THE EDITORS ON THE DETERMINATION OF INCLUSIONS IN CRYSTALS GROWN FROM AQUEOUS SOLUTIONS H. LOOSER, M. EHRENSPERGER and H. AREND Laboratory of Solid State Physics, Swiss Federal Institute of Technology, CH- 8093 Zurick Switzerland Received 3 June 1985
Growth solution inclusions were determined in gel grown PbHPO
4 crystals by means of differential scanning calorimetry. The
detection limit corresponds to 20 ppm H 20.
A characteristic imperfection in solution grown crystals are inclusions of the mother solution from which the crystals wee grown. Even small amounts of such inclusions, which are sometimes difficult to detect, can drastically influence important properties of their “host” crystal. Such effects were observed, e.g., in non-transparent 2 Pt(CN4)Br04 3.2H2O crystals where an extremely high mobility of Br ions was erroneously deduced from NMR signals due to Br ions in aqueous solution inclusions [1,2]. Recently Nelmes and Lockwood detected anomalous transition-like effects in PbHPO4 I
3.0
I
I
I
slightly below 273 K, in addition to the well known para-ferroelectric phase transition at 308 K [3]. Differential scanning calorimetry (DSC) scans of gel grown crystal platelets revealed typical peaks of a phase transition (fig. 1) in this temperature range. The phase transition was of first order, as could be deduced from a strong hysteresis effect in heating and cooling runs. In order to elucidate the nature of this effect the following experiments were made: (1) A series of about 10 samples weighing from 78 to 144 mg were examined and the intensity of the effect varied from sample to sample. I
-
~: ~ 230
250
270 290 Temperature [K]
310
330
Fig. 1. DSC scan of a gel grown PbHPO4 crystal. Scan rate 5.0 K/mm, crystal weig~it144 mg, 7~= 309 K, T~’(anomalous transition) = 269 K.
0022-0248/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
744
H. Looser et aL
/
Determination ofinclusions in crystals
(2) In PbDPO4 crystals, in which the para-ferroelectric transition is strongly shifted to higher temperatures, only a negligible shift of the anomalous effect was observed. (3) Upon heating to 450 K for 1 h the anomalous peak disappeared. These results are clear evidence that the additional peaks are due to solution inclusions. From the transition enthalpy one can calculate the amount of solvent in the crystals. The smallest amount which we were able to detect in any sample by means of a Perkin-Elmer DSC2 calorimeter corresponds to 1 ~tg or 20 ppm by weight.
Thus it is evident that differential scanning calorimetry is a very useful tool for the detection of even small amounts of aqueous solution inclusions. The described technique demands however the use of small samples with dimensions limited by the type of the measuring cell used.
References [1) H. Nagasawa and N. Miyauchi. Phys. Status. Solidi (b) 71 (1975) 671. . [2] D. Bnnkmann, G. Finger and H. Arend, Phys. Status Solidi (b) 83 (1977) 1(45. [3] R. Nelmes and D.J. Lockwood, private communication.