Paola caballero and anthony hernandez solid state synthesis manuscript

Scientific Manuscript 2014

Abstract

There is strong interest in the unique

properties of inorganic solids that can be

utilized for a whole array of

technological applications such as

functioning as semiconductors and

catalysts. High temperature synthesis

will be utilized as the means for

obtaining novel inorganic solid phase

materials, specifically mixed-metal

oxides. Although widely used, this

procedure has to be categorized as a

trial and error based method. Products

are predicted through established

stoichiometry of the reactants. Further

characterization by means of X-ray

crystallography will provide with the

exact composition and stoichiometry of

the inorganic solid. Due to some

limitations, the reactions and products

were predicted but the synthesis part of

the project was not carried out.

1. Introduction

Modern electronic technology is

completely dependent on the properties

that specific solid substances exhibit.

One of the most active research fields in

our technological era is Solid State

Chemistry. This branch, also called

materials science, focuses on

synthesizing new metal compounds that

may result in crystalline solids. There is

strong interest in the unique magnetic,

electrical, optical, and catalytic

properties of these inorganic solids that

can be utilized for a whole array of

technological applications. Inorganic

materials are used to manufacture

devices such as semiconductors, which

are the devices that serve as the

foundation for all solid state electronic

such as transistors, silicon chips, photo

cells, and others (Cotton et. al 1995).

Solid state synthesis is usually carried

out in two distinct ways. One common

method involves mixing the reactants in

their liquid form (or aqueous solution,

depending on the solvent) so that a

chemical reaction takes place and the

solid product precipitates. The second

method, which is the one that will be

utilized during our research, is one of

the simplest and most widely used

procedures (Cotton et. al 1995). It

consists of using high temperature

reactions that require mixing two or

more finely powdered starting materials,

placing the mixture inside a sealed

container and then heating this same

container in a specialized oven at

>500˚C in order to obtain inorganic

compounds, especially in crystalline

form. Although simple and widely used,

this method has various shortcomings

that must be addressed. The main

disadvantage is that it is usually

challenging to predict the stoichiometry

of the product(s), resulting in an almost

Solid-State Synthesis of Mixed-Metal Oxides Paola G. Caballero León1, Anthony Hernández Rivera2

1Department of Chemistry, RISE Program, University of Puerto Rico at Cayey 2Department of Biology, RISE Program, University of Puerto Rico at Cayey


trial and error based method. For this

reason, this specific branch of research

is often described as mostly exploratory

science. Having calculated a total of 10

reactions from groups 14/15, 14/14,

15/15 using the available finely

powdered starting materials available at

the laboratory, we now plan to

synthesize inorganic compounds and

analyze if the final products resemble

one of the possibilities that were initially

calculated. The stoichiometry of one of

the reactions with metals from group 14

and 15 was established so that one of

the products would have a pyrochloric

structure. A mixed metal oxide

compound with a pyrochloric structure

has a stoichiometry of A2B2O7, in which

the letters A and B represent two metals

(Jones and Knight 1997). According to

Salamat et al. (2011) solids with

pyrochloric have important dielectric

properties that make them essential in

the production of thin film devices and

are being used for microwave

applications. Most importantly we aim to

obtain solid inorganic compounds as our

final product, ideally in crystalline form,

that exhibit magnetic, electrical or other

unique properties that have variety of

technological applications.

2. Materials and Methods

2.1. Predicting Products

Two metals- Sn, Sb, Bi, or Pb -

were chosen as the primary reactants.

The stoichiometry of the metals was

established for further calculations. For

example, 4Sn: 3Bi is a reaction where

the stoichiometry of the reactants is 4

atoms of Sn for each 3 atoms of Bi.

Once the stoichiometry was determined,

all possible products were predicted. In

order to do this, the oxidation number of

each reactant was taken under

consideration. In the previous example,

Sn has two possible oxidation numbers:

+2 and +4. On the other hand, Bi only

has the oxidation number +3. Therefore,

there are only two possible products for

such reaction: 4Sn+2:3Bi+3 and 4Sn+4:

3Bi+3. The positive charges were

summed up to determine how many

oxygen atoms are needed in order to

predict a neutral compound. The oxygen

atoms from the air react with the

reactants. Oxygen has an oxidation

number of -2. This negative charge will

balance out the positive charges from

the metals. In the first combination of

the example, the sum of the positive

charges is (+8) + (+6) for a total charge

of +14. Therefore, seven oxygen atoms

are required because (7) x (-2) is equal

to -14. The overall charge of the

predicted compound is then (+14) + (-

14) which is equal to 0, in other words, it

is neutral.

Once the whole array of possible

products was predicted from simple

stoichiometry, the amount of the

reactants to be loaded was calculated.

The mass of the heaviest element was

calculated from 20 mg of the lightest

element and the established

stoichiometry. With these calculations,

the reaction mixture can be properly

prepared.

2.2. Preparation of Silica Tubes


A long silica tube was cut into eight

12 inch smaller tubes. Each of these

tubes was divided into two smaller tubes

with the use of an acetylene flame.

Afterwards, the bottom part of each tube

was molded with the acetylene flame so

that it was completely sealed. Three

drops of acetone were added to the

tube. With the use of a Bunsen burner,

the bottom of the tube was heated up

until the acetone evaporated and a

single carbon layer formed on the inside

of the tube. The process was repeated

three times in order to obtain a three

layer carbon lining, each one higher

than the last. This serves to isolate the

reactants from the silica and ensure the

reaction happens as predicted.

Subsequently, the reactants were added

to the tube and stored for further

processing.

2.3. High Temperature Reaction

Once the finely powdered reactants are

added to the tube, the mixture will be

subject to a high temperature reaction in

order to obtain novel mixed metal oxide

crystals. Basically, the mixture is

heated up in an oven designed to

withstand high temperatures until both

reactants change to their liquid phases.

This part of the process can last for a

period of three weeks. Afterwards, the

solution is cooled down slowly, to permit

the formation of crystals. Although the

procedure is rather simple, it is also time

consuming. Due to some limitations, this

part of the project was not carried out.

3. Results

3.1. Predicting Products

Ten reactions were calculated using

metals from groups 14 and 15. The

stoichiometry for each reaction was

determined and the products were

predicted. The predicted products for

the mixing of same group metals (14/14

and 15/15) are summarized in table 1.

Group 14/14

1) 9Sn: 15Pb

Reactants Products

9Sn+2, 15Pb+2 Sn9Pb15O24

9Sn+2, 15Pb+4 Sn9Pb15O39

9Sn+4, 15Pb+2 Sn9Pb15O33

9Sn+4, 15Pb+4 Sn9Pb15O48

2) 3Sn: 5Pb

Reactants Products

3Sn+2, 5Pb+2 Sn3Pb5O8




3) 13Sn: 6Pb

Reactants Products

13Sn+2, 6Pb+2 Sn13Pb6O19

13Sn+2, 6Pb+4 Sn13Pb6O25

13Sn+4, 6Pb+2 Sn13Pb6O32

13Sn+4, 6Pb+4 Sn13Pb6O38

Group 15/15

4)7Sb: 21Bi

Reactants Products

7Sb+3, 21Bi+3 Sb7Bi21O42

7Sb+5, 21Bi+3 Sb7Bi21O49

5) 11Sb: 3Bi

Reactants Products

11Sb+3, 3Bi+3 Sb11Bi3O21

Table 1: Mixed

Metal Oxide

reactions from

groups 14/14

and 15/15 and

their

respective

predicted

compounds.


11Sb+5, 3Bi+3 Sb11Bi3O32

The predicted products for the mixing of

mixed group metals (14/15) are

summarized in table 2.

Group 14/15

1) 7Bi:9Sn

Reactants Products

7Bi+3 , 9Sn+2 Bi14Sn18O39

7Bi+3 , 9Sn+4 Bi14Sn18O57

2) 13Pb:23Bi

Reactants Products

13Pb+2, 23Bi+3 Pb26Bi46O95

13Pb+4, 23Bi+3 Pb26Bi46O121

3) 33Pb:21Sb

Reactants Products

33Pb+2, 21Sb+3 Pb66Sb42O129

33Pb+2, 21Sb+5 Pb66Sb42O171

33Pb+4, 21Sb+3 Pb66Sb42O195

33Pb+4, 21Sb+5 Pb66Sb42O237

4)12Sn: 17Sb

Reactants Products

12Sn+2, 17Sb+3 Sn24Sb34O75

12Sn+2, 17Sb+5 Sn24Sb34O109

12Sn+4, 17Sb+3 Sn24Sb34O99

12Sn+4, 17Sb+5 Sn24Sb34O133

5) 2Sn:2Bi

Reactants Products

2Sn+2, 2Bi+3 Bi2Sn2O5

2Sn+4, 2Bi+3 Bi2Sn2O7

3.2. High Temperature Reaction

There were some limitations that

impeded us to obtain results. The main

obstacle was that the oven’s lid was not

available. Therefore, the oven was non-

functional and none of the reactions

could be loaded for further processing.

The secondary obstacle was the time

constraint to carry out the project, which

was partially completed.

4. Future Work

Due to time constraints and a non-

operational oven we will put on hold our

project until the appropriate parts of the

oven arrive and are installed. After this

we intend to load our respective

reactions using the finely powdered

starting materials available at the

laboratory, elements: Sn, Pb, Sb, and Bi

(groups 14/15, 14/14, and 15/15). We

will then proceed to synthesizing new

solid inorganic compounds in

accordance with the established

reactions.

5. Acknowledgements

We would like to give special thanks to

RISE Program for this great research

project that has once more enabled us

to gained invaluable laboratory and

research experience. Also we highly

appreciate our research mentor Dr.

Lukasz Koscielski and Teaching

Assistant (TA) Gerardo Ramos.

Literature Cited

Table 2: Mixed

Metal Oxide

reactions from

groups 14/15

and the

respective

predicted

compounds.


Adams DM. 1986. Sólidos Inorgánicos.

1st edition. Madrid. Alhambra Editorial.

Cotton FA, Wilkinson G, Gaus PL. 1995.

Basic Inorganic Chemistry. 3rd edition.

New York. John Wiley & Sons, Inc.

Jones RH, Knight KS. 1997. The

structure of ã-Bi2Sn2O7 at 725 8C

by high-resolution neutron diffraction:

implications for bismuth(III)-containing

pyrochlores. J. Chem. Soc. 2551-2555

Salamat A, Hector AL, McMillan PF,

Ritter C. 2011. Structure, Bonding, and

Phase Relations in Bi2Sn2O7 and

Bi2Ti2O7 Pyrochlores: New Insights

from High Pressure and High

Temperature Studies. Inorg. Chem.

11905-11913.

Paola caballero and anthony hernandez solid state synthesis manuscript

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