Synthesis and Characterization of a Pb1-xSrxCrO4 Solid Solution

Ohio State UniversityCHEM 123 REEL Poster Session

Matthew W. StoltzfusThad MattaJim TresselBob Todd

22 May 2007

Goals

What are the goals of your research. What scientific concepts are you trying to understand?

What pigments are you trying to replace and why?

Pb(SbO3)2 CdS PbCrO4

Traditional pigments:

Synthesis: End Members

2 PbCO3 + Cr2O3 + 3/2 O2 2 PbCrO4 + 2 CO2

Cr2O3 + 2 SrCO3 + 3/2 O2 2 SrCrO4 + 2 CO2

9 PbCO3 + 5 Cr2O3 + SrCO3 + 15/2 O2 10 Pb0.9Sr0.1CrO4 + 10 CO2

8 PbCO3 + 5 Cr2O3 + 2 SrCO3 + 15/2 O2 10 Pb0.8Sr0.2CrO4 + 10 CO2

5 PbCO3 + 5 Cr2O3 + 5 SrCO3 + 15/2 O2 10 Pb0.5Sr0.5CrO4 + 10 CO2

2 PbCO3 + 5 Cr2O3 + 8 SrCO3 + 15/2 O2 10 Pb0.2Sr0.8CrO4 + 10 CO2

PbCO3 + 5 Cr2O3 + 9 SrCO3 + 15/2 O2 10 Pb0.1Sr0.9CrO4 + 10 CO2

All reactions were carried out using traditional solid state synthesis overnight at 750°C.

Synthesis: Solid Solution

2 PbCO3 + Cr2O3 + 3/2 O2 2 PbCrO4 + 2 CO2

Cr2O3 + 2 SrCO3 + 3/2 O2 2 SrCrO4 + 2 CO2

9 PbCO3 + 5 Cr2O3 + SrCO3 + 15/2 O2 10 Pb0.9Sr0.1CrO4 + 10 CO2

8 PbCO3 + 5 Cr2O3 + 2 SrCO3 + 15/2 O2 10 Pb0.8Sr0.2CrO4 + 10 CO2

5 PbCO3 + 5 Cr2O3 + 5 SrCO3 + 15/2 O2 10 Pb0.5Sr0.5CrO4 + 10 CO2

2 PbCO3 + 5 Cr2O3 + 8 SrCO3 + 15/2 O2 10 Pb0.2Sr0.8CrO4 + 10 CO2

PbCO3 + 5 Cr2O3 + 9 SrCO3 + 15/2 O2 10 Pb0.1Sr0.9CrO4 + 10 CO2

All reactions were carried out using traditional solid state synthesis overnight at 750°C.

Color and UV-Vis Spectra: End Members

PbCrO4 SrCrO4Pb0.9Sr0.1CrO4 Pb0.8Sr0.2CrO4 Pb0.5Sr0.5CrO4 Pb0.2Sr0.8CrO4 Pb0.1Sr0.9CrO4

0

10

20

30

40

50

60

70

80

90

100

400 450 500 550 600 650 700 750

Wavelength (nm)

Ref

lect

ance

PbCrO4

Pb(0.9)Sr(0.1)CrO4

Pb(0.8)Sr(0.2)CrO4

Pb(0.5)Sr(0.5)CrO4

Pb(0.2)Sr(0.8)CrO4

Pb(0.1)Sr(0.9)CrO4

SrCrO4

Color and UV-Vis Spectra: Solid Solution

PbCrO4 SrCrO4Pb0.9Sr0.1CrO4 Pb0.8Sr0.2CrO4 Pb0.5Sr0.5CrO4 Pb0.2Sr0.8CrO4 Pb0.1Sr0.9CrO4

0

10

20

30

40

50

60

70

80

90

100

400 450 500 550 600 650 700 750

Wavelength (nm)

Ref

lect

ance

PbCrO4

Pb(0.9)Sr(0.1)CrO4

Pb(0.8)Sr(0.2)CrO4

Pb(0.5)Sr(0.5)CrO4

Pb(0.2)Sr(0.8)CrO4

Pb(0.1)Sr(0.9)CrO4

SrCrO4

X-Ray Diffraction Data: Solid Solution

20 22 24 26 28 30 32 34 36 38 40

PbCrO4 Pb0.9Sr0.1CrO4 Pb0.8Sr0.2CrO4 Pb0.5Sr0.5CrO4 Pb0.2Sr0.8CrO4 Pb0.1Sr0.9CrO4 SrCrO4

SrCrO4

PbCrO4

The XRD patterns show the SrCrO4 and PbCrO4 form a complete solid solution from x = 0.0 to x = 1.0.

Isothermal Phase Diagram: Solid Solution

SrCrOSrCrO44PbCrOPbCrO44

Complete Solid Solution, Pb1-xSrxMoO4

Increasing Sr

x=0 x=0.2 x=0.5 x=0.8 x=1.0

SrSr PbPb CrOCrO44

Monoclinic Monoclinic

Origins of Color

What electronic excitations are responsible for color in each of your end members?

What electronic excitations are responsible for color across your solid solution? Why/how might you expect the color to vary across the solid solution?

Band Gaps (or Absorption Peaks)

PbCrO4 SrCrO4Pb0.9Sr0.1CrO4 Pb0.8Sr0.2CrO4 Pb0.5Sr0.5CrO4 Pb0.2Sr0.8CrO4 Pb0.1Sr0.9CrO4

2.27 eV 2.27 eV 2.32 eV 2.41 eV 2.48 eV 2.50 eV 2.53 eV

Band Gap as a Function of Composition

2.25

2.30

2.35

2.40

2.45

2.50

2.55

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Composition of x

Ban

d G

ap (e

V)

Be sure to define which composition corresponds to x = 0 and which to x = 1.

Conclusions and Future Directions

Did you form a solid solution? If so over what composition ranges?

What colors were your samples? Are the colors what you would expect from the UV-Vis spectra? How did the band gap vary as a function of composition? Would these samples make good pigments?

What would you do next to reach the goal stated on the first slide? What other compositions might be tried? What have you learned about the relationship between composition, optical absorption and color?